Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

Wettability and wetting characterisation of ultrafine glass particles for particle separation technologies

Sandbrink, J.; Rudolph, M.

Many particle separation processes are based on differences in wettabilities. Therefore, one needs to understand the interfacial properties and micro processes taking place on the material surface. The main quantity to account for wettability is the Young contact angle. However, this method requiring homogeneous flat and smooth substrates has drawbacks when analysing particles and is rather system specific as particles are not planar and exhibit rough surfaces. Here, we demonstrate the challenges of proper wettability analysis of particulate material as available methods are influenced strongly by multiple particle properties such as shape and size. Three fractions of glass particles with different shapes are investigated, fibres, fragments, spheres, and their wettability is modified by esterification with alcohols. These particle systems are characterised via analytic particle solvent extraction, static and dynamic contact angle measurements, and inverse gas chromatography. Alcohols with longer alkyl chains result in more hydrophobic particles with more homogeneous wettability characteristics in terms of surface energy. Comparing the characterisation methods reveals the influence of particle morphology on the interfacial wetting behaviour. Applying inverse gas chromatography for wettability characterisation in combination with the other methods underlines its potentials as well as limitations in understanding particulate surface properties.

Keywords: Wettability; Hydrophobicity; Surface heterogeneity; Surface free energy; Inverse gas chromatography; Contact angle

  • Invited lecture (Conferences) (Online presentation)
    2nd European Sorption Science Symposium 2021, 22.-23.09.2021, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-33461
Publ.-Id: 33461


Numerical and experimental methods for the analysis of complex particulate systems

Lecrivain, G.; Hampel, U.

In this presentation, experimental and numerical tools available at HZDR are presented for the analysis of complex particulate systems. Energy-intensive particulate systems includes, for example, high-temperature reactors, mixers for the mineral and cement industries, flotation apparatuses for the selective of separation minerals, textile fibers, micro-algae as well as plastics.

Keywords: Particle transport; Resource efficiency; Particulate systems

  • Lecture (Conference)
    M0-Workshop des Topic 5 „Ressourcen- und Energieeffizienz“ des Helmholtz-Programms Materialien und Technologien für die Energiewende, 18.11.2021, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-33460
Publ.-Id: 33460


Particle deposition and resuspension in turbulent gas flows - An industrial and environnemental application

Lecrivain, G.

The talk will focus on the transport, deposition and resuspension of particles in the micron size in air systems. Expertise of the Helmholtz-Zentrum Dresden-Rossendorf in the experimental and numerical investigation of particle-laden flow will be presented. A first application includes the transport of dust particles in industrial systems. A second application is the resuspension of toxic micronparticles in urban system by strong winds. In these two scenarios, experimental tests are first used to study small-scale mechanisms. Simulations are then used to extrapolate the much larger systems.

Keywords: Particle transport; Microplastics; Turbulent flows

  • Lecture (others) (Online presentation)
    Workshop on microplastics in the atmosphere, 22.11.2021, Valbonne, France

Permalink: https://www.hzdr.de/publications/Publ-33459
Publ.-Id: 33459


Estimating uncertainties of radionuclide migration in crystalline host rock - an interdisciplinary approach

Pospiech, S.; Brendler, V.

Estimating uncertainties of radionuclide migration in crystalline host rock - an interdisciplinary approach

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2022
    119
    41 Seiten
    ISSN: 2191-8708, eISSN: 2191-8716
    ISSN: 2191-8716
    ISSN: 2191-8708

Permalink: https://www.hzdr.de/publications/Publ-33458
Publ.-Id: 33458


Autocorrected off-axis holography of two-dimensional materials

Kern, F.; Linck, M.; Wolf, D.; Alem, N.; Arora, H.; Gemming, S.; Erbe, A.; Zettl, A.; Büchner, B.; Lubk, A.

The reduced dimensionality in two-dimensional materials leads to a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high-resolution microscopy techniques are indispensable. Here we report on the development of an electron holography (EH) transmission electron microscopy (TEM) technique, which facilitates high spatial resolution by an automatic correction of geometric aberrations. Distinguished features of EH beyond conventional TEM imaging are gap-free spatial information signal transfer and higher dose efficiency for certain spatial frequency bands as well as direct access to the projected electrostatic potential of the two-dimensional material. We demonstrate these features with the example of h-BN, for which we measure the electrostatic potential as a function of layer number down to the monolayer limit and obtain evidence for a systematic increase of the potential at the zig-zag edges.

Permalink: https://www.hzdr.de/publications/Publ-33457
Publ.-Id: 33457


Radiosynthesis and biological investigation of an 18F-labeled triazolopyridopyrazine-based inhibitor for imaging of the phosphodiesterase 2A enzyme (PDE2A) in brain

Wenzel, B.; Fritzsche, S. R.; Deuther-Conrad, W.; Toussaint, M.; Briel, D.; Kopka, K.; Brust, P.; Scheunemann, M.

Objectives: The cyclic nucleotide phosphodiesterase 2A is an intracellular enzyme which hydrolyzes the second messengers cAMP and cGMP and therefore plays an important role in signaling processes. It is highly expressed in distinct brain areas associated with emotion, memory and learning. Therefore, it is assumed that the PDE2A is involved in the pathophysiology of neurodegenerative and neuropsychiatric diseases. To enable a specific imaging of this enzyme in the brain by PET, we are developing fluorine-18 labeled radioligands with high inhibitory potency and selectivity toward other phosphodiesterases, in particular the PDE10A, which is also located in typical PDE2A-rich brain regions.

Methods: Out of a series of 12 tricyclic triazolopyridopyrazine-based derivatives with high inhibitory potency toward PDE2A and selectivity vs. PDE10A [1], the most promising candidate 1 was selected for radiofluorination. The radiolabeling was performed in a two-step one-pot procedure via nucleophilic aromatic substitution of the nitro group (precursor 2) by [18F]fluoride followed by the reduction of the activating ketone function to obtain the desired radiotracer [18F]1 (Figure 1). The product was isolated using semi-preparative HPLC followed by final purification with solid-phase extraction and formulation in isotonic saline containing 10% ethanol. In vitro autoradiography studies with cryosections of rat brain and PET studies in female Sprague-Dawley rats (30 min dynamic PET imaging after intravenous injection, nanoScan® PET/MRI, MEDISO, Budapest, Hungary) were performed. The in vivo metabolism of [18F]1 was investigated by radio-HPLC analysis of extracts obtained from blood plasma and homogenized brain of rats at 30 min p.i.

Results: The new derivative 1 inhibits PDE2A with high potency (IC50 PDE2A3 = 1.99 nM) and superior selectivity against PDE10A (IC50 PDE10A1 = 1910 nM). [18F]1 was obtained with a radiochemical yield of 2.1 ± 0.7% (EOB), molar activities of 10–20 GBq/µmol (EOS) and radiochemical purities of ≥ 99% (n=7). The distribution pattern of [18F]1 detected by in vitro autoradiography corresponds to the anatomical distribution of PDE2A in rat brain with prominent expression in the superficial layers of the somatosensory cortex, in hippocampal structures, and in basal ganglia, and with nearly no expression in the cerebellum. By co-incubation with compound 1 as well as two structurally different well-established PDE2A inhibitors, the binding of [18F]1 was completely inhibited, confirming the high specific interaction with PDE2A. In vivo PET-MR studies revealed a good brain uptake (SUV peak = 1.0); however, a considerable enrichment in PDE2A-specific regions was not detectable (15 min p.i.: SUVcaudate putamen = 0.51 vs. SUVcerebellum = 0.40). Furthermore, in vivo metabolism studies of [18F]1 revealed unneglectable fractions of radiometabolites in blood plasma and brain at 30 min p.i. (parent compound: 50 and 66%, resp.).

Conclusions: [18F]1 is a suitable and high specific probe for the investigation of the PDE2A expression in vitro. However, further work is needed to explore the reasons for the poor in vivo imaging capability of this radiotracer.

Acknowledgment: Deutsche Forschungsgemeinschaft (German Research Foundation, SCHE 1825/3-1).

References: [1] S. R. Fritzsche et al. „Triazolopyridopyrazine-based Inhibitors of Phosphodiesterase 2A – Synthesis and SAR-Exploration“, Annual Meeting of the German Pharmaceutical Society – DPhG 2021, Poster

  • Poster
    24th International Symposium on Radiopharmaceutical Sciences, 29.05.-02.06.2022, Nantes, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-33456
Publ.-Id: 33456


Prograde and retrograde precession of a fluid-filled cylinder

Pizzi, F.; Giesecke, A.; Simkanin, J.; Stefani, F.

We numerically study precession driven flows in a cylindrical container whose nutation angle varies between 60 and 90 degrees for prograde and retrograde precession. For prograde precession we observe sharp transitions between a laminar and a turbulent flow state with low and high geostrophic axisymmetric flow components related with a centrifugal instability, while for retrograde precession a rather smooth transition between a low state and a high state occurs. At the same time prograde and perpendicular precession shows an abrupt breakdown of the flow directly excited by the forcing mechanism, which is not the case for retrograde motion. We characterize the corresponding flow states in terms of the directly driven, non-axisymmetric Kelvin mode, the axisymmetric geostrophic mode, and an axisymmetric poloidal flow which is promising for precession-driven dynamo action. The latter issue is discussed with particular view on an optimal parameter choice for the DRESDYN dynamo project.

Keywords: precession; core flow; dynamo; instability; transition

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Permalink: https://www.hzdr.de/publications/Publ-33455
Publ.-Id: 33455


Oxidation of Micro- and Nanograined UO2Pellets by in Situ Synchrotron X-ray Diffraction

de Bona, E.; Popa, K.; Walter, O.; Cologna, M.; Hennig, C.; Scheinost, A.; Prieur, D.

When in contact with oxidising media, UO2 pellets used as nuclear fuel may transform into U4O9, U3O7, and U3O8. The latter starts forming by stress-induced phase transformation only upon cracking of the pristine U3O7, and is associated with a 36 % volumetric expansion with respect to the initial UO2. This may pose a safety issue for spent nuclear fuel (SNF) management as it could imply a confinement failure and hence dispersion of radionuclides within the environment. In this work, UO2 with different grain sizes (representative of the grain size in different radial positions in the SNF) were oxidised in air at 300 °C, and the oxidation mechanisms were investigated using in-situ synchrotron XRD. The formation of U3O8 was detected only in UO2 pellets with larger grains (3.08 ± 0.06 µm and 478 ± 17 nm), while U3O8 did not develop in sintered UO2 with a grain size of 163 ± 9 nm. This result shows that, in dense materials, a sufficiently fine microstructure inhibits both the cracking of U3O7 and the subsequent formation of U3O8. Hence, the nanostructure prevents the material from undergoing significant volumetric expansion. Considering that the peripheral region of SNF is constituted by the High Burnup Structure (HBS), characterised by 100-300 nm sized grains and micrometric porosity, these findings are relevant for a better understanding of the spent nuclear fuel behaviour and hence for the safety of the nuclear waste storage.

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Permalink: https://www.hzdr.de/publications/Publ-33454
Publ.-Id: 33454


Higher harmonics in complex plasmas with alternating screening

Moldabekov, Z.; Aldakul, Y. K.; Bastykova, N. K.; Sundar, S.; Cangi, A.

We report how higher harmonics of collective excitations emerge in a 2D layer of strongly correlated charged microparticles in a complex plasma with a periodically alternating screening.
The simulation results of the radio frequency discharge and the charged microparticles are obtained using a highly accurate multi-scale and multi-physics approach based on the particle-in-cell technique, Monte Carlo collision calculations, and molecular dynamics simulations.
We also devise a simple phenomenological expression for the dispersion relation of higher harmonics.
Furthermore, our analysis reveals that the periodically alternating screening causes a self-conjugate state with negative refraction.
In doing so, we demonstrate how complex plasmas can serve as a testbed for studying the fundamental physics of a self-conjugate state in strongly correlated systems.

Keywords: plasma physics; strongly correlated plasmas; complex plasmas

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Permalink: https://www.hzdr.de/publications/Publ-33453
Publ.-Id: 33453


Data publication: Controlled Silicidation of SiNW using FLA

Khan, M. B.; Prucnal, S.; Ghosh, S.; Deb, D.; Hübner, R.; Pohl, D.; Rebohle, L.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

The folder contains the following: 1. all the SEM and TEM images. 2. The schematics of fabrication 3. comparison of silicidation with FLA and RTA and 4. temperature simulations to estimate temperature during FLA process.

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Permalink: https://www.hzdr.de/publications/Publ-33452
Publ.-Id: 33452


Effect of Interfacial Defects on the Electronic Properties of MoS₂ Based Lateral T-H Heterophase Junctions

Bahmani, M.; Ghorbani Asl, M.; Frauenheim, T.

The coexistence of semiconducting (2H) and metallic (1T) phases of MoS₂ monolayers have further pushed their strong potential for applications in the next generation of electronic devices based on two-dimensional lateral heterojunctions. Structural defects have considerable effects on the properties of these 2D devices. In particular, the interfaces of two phases are often imperfect and may contain numerous vacancies created by phase engineering techniques, e.g. under the electron beam. Here, the transport behaviors of the heterojunctions in the existence of point defects are explored by means of first-principles calculations and non-equilibrium Green's function approach. While vacancies in semiconducting MoS₂ act as scattering centers, their presence at the interface improves the flow of the charge carriers. In the case of Vmo, the current has been increased by two orders of magnitude in comparison to the perfect device. The enhancement of transmission was explained by changes in the electronic densities at the T-H interface, which open new transport channels for electron conduction.

Keywords: two-dimensional materials; defects; lateral heterostructure; conductivity; quantum transport; DFT

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Permalink: https://www.hzdr.de/publications/Publ-33451
Publ.-Id: 33451


Direct visualization of highly resistive areas in GaN by means of low-voltage scanning electron microscopy

Jóźwik, I.; Jagielski, J.; Caban, P.; Kamiński, M.; Kentsch, U.

The damage-induced voltage alteration (DIVA) contrast mechanism in scanning
electron microscope (SEM) at low electron energy has been presented as a fast and
convenient method of direct visualization of increased resistivity induced by energetic
ions irradiation in gallium nitride (GaN). Epitaxially grown GaN layers on sapphire
covered with a metallic masks with etched windows were subjected to He 2+
irradiations at 600 keV energy. The resulting two-dimensional damage profiles at the
samples cross-sections were imaged at SEM at different e-beam energies and scan
speeds. The gradual development of image contrast was observed with the increase of
cumulative charge deposited by electron beam irradiation, to finally reach the
saturation level of the contrast related to the local resistivity of the ion-irradiated part of
GaN.
The presented method allows one to directly visualize the ion-irradiated zone even for
the lowest resistivity changes resulting from ion damage, i.e. all levels of insulation
build-up in GaN upon irradiation with ions. Taking into account that it is not possible to
apply the etch-stop technique by wet chemistry to GaN, it makes the presented
technique the only available method of visualization of highly resistant and insulating
regions in GaN-based electronic devices.
Main aim of the presented work is to get a deeper insight into a DIVA contrast in GaN
with the special emphasize to discuss the role of rastering speed and electron beam
current, i.e. details of charge build-up ion the sample surface.

Keywords: GaN; Ion damage; Ion implantation; Low-kV SEM

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Permalink: https://www.hzdr.de/publications/Publ-33450
Publ.-Id: 33450


Small-angle neutron scattering applied to low-dose neutron-irradiated Fe–Cr alloys and ferritic martensitic steel Eurofer97

Ulbricht, A.; Heinemann, A.; Bergner, F.

Abstract Experimental results reported before for neutron-irradiated binary Fe-Cr alloys and high-dose neutron-irradiated ferritic/martensitic (F/M) Cr steels do not unfold a complete understanding of the irradiation behaviour required for the application of F/M steels in nuclear components. Gaps are related to the effect of secondary alloying and impurity elements, such as Ni and Si, as well as the dose dependence at lower neutron doses, e.g. the range 0.1 – 1 displacements per atom (dpa). Such input is essential for both multiscale modelling of irradiation effects and the evaluation of nuclear fission or fusion components at the first stages of operation. Using magnetic small-angle neutron scattering, three pieces are added to the puzzle: (1) The effect of Cr undersaturation (5% Cr) and supersaturation (14% Cr) on the formation of irradiation-induced solute atom clusters/precipitates in the presence of intentionally added levels of Ni, Si, and P; (2) the effect of irradiation temperature, 290 °C versus 450 °C; and (3) a comparison of two heats of Eurofer 97, one of them neutron-irradiated to 0.06, 0.1 and 0.6 dpa. We have found that the irradiation-enhanced formation of Cr-rich α’-phase particles is the dominant effect for supersaturated Fe-14Cr-NiSiP. In contrast, α’ formation is impossible in Fe-5Cr-NiSiP, for which the pronounced irradiation effects observed at 0.1 dpa are mainly due to added Ni, Si and P. Finally, the 9Cr steel Eurofer 97 exhibits a much smaller irradiation effect than Fe-9Cr-NiSiP. The reasons of this exceptional irradiation resistance are discussed.

Keywords: Small-angle neutron scattering; Fe-Cr alloys; Ferritic-martensitic steel; Neutron irradiation

Permalink: https://www.hzdr.de/publications/Publ-33449
Publ.-Id: 33449


Process simulation for comprehensive sustainability assessment of the silicon photovoltaic life cycle

Bartie, N.; Cobos-Becerra, L.; Froehling, M.; Schlatmann, R.; Reuter, M.

Over the last decade, the global solar PV industry has grown at a rate of more than 35% annually, reaching record levels and outpacing annual conventional power capacity additions and will continue its trajectory to reach terawatt-level deployment by 2022-2023 and an estimated 8.5 TW (cumulative) by 2050. The global c-Si cell and PV module production capacity at the end of 2020 is assumed to have further increased to over 200 GWp due to continued PERC capacity expansion. To assess the potential contribution photovoltaics (PV) can make to decarbonization, and to achieving the European and global sustainable development and circular economy goals, the resource efficiency and sustainability of photovoltaic life cycle systems need to be evaluated. Using process simulation, we create detailed digital representations of entire PV life cycles. These include all raw material and PV production steps, as well as recycling processes that close material loops and aim to recover valuable materials from end-of-life modules. The simulations make use of the physical, chemical, and thermodynamic processes that govern each step in the life cycle to deliver a robust foundation from which to determine the potential impacts of individual processes and the system on resource consumption, resource efficiency, the environment, and technoeconomic parameters. In this paper, we focus on the assessment of potential recycling, wafer thickness, and carbon tax effects on the resource efficiency, carbon footprint, and technoeconomic performance of the system.

Keywords: Silicon PV system; LCOE; MSP; resource efficiency; carbon footprint; recycling; simulation

Permalink: https://www.hzdr.de/publications/Publ-33448
Publ.-Id: 33448


Coordination and Electrochemical Switching on Paddle-Wheel Complexes Containing an As−Ru or a Sb−Ru Axis

Gericke, R.; Wagler, J.

Inspired by the known complex [PhP(μ-PyO)₄Ru(CO)] (PyO = 2-pyridyloxy), the family of group 15 paddle-wheel complexes has been expanded to [PhPn(μ-PyO)₄Ru(L)] (Pn = P, As, Sb; L = NCMe, CO). Solvent-dependent reversible switching between [PhAs(μ-PyO)₄Ru(NCMe)] and [PhAs(μ-PyO)₃Ru(κ²-PyO)] was detected. Electrochemical investigations of the [PhPn(μ-PyO)₄Ru(L)] complexes showed reversible oxidation of the complexes with L = NCMe and back-formation of the complexes with L = NCMe upon oxidation of the complexes with L = CO in NCMe. In the series of [PhPn(μ-PyO)₄RuL)] complexes, the Pn→Ru bonding mode is shifted from L-type Pn to X-type upon going from Pn = P and As to Pn = Sb, resulting in a pronounced electron-rich Ru site in the latter case. The easily accessible complex [PhSb(μ-PyO)₄RuCl] exhibits reversible electrochemical and coordinative exchange with its reduced analogue [PhSb(μ-PyO)₄Ru(NCMe)] under retention of the paddle-wheel motif and Sb−Ru bond properties.

Keywords: ambidentate ligands; ruthenium; pnictogen; hetero bimetallic; electrochemical switching

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-33447
Publ.-Id: 33447


The precession dynamo experiment at HZDR

Giesecke, A.; Pizzi, F.; Kumar, V.; Anders, S.; Ratajczak, M.; Gundrum, T.; Stefani, F.

Cosmic magnetic fields exist on all scales, from planets and stars to
galaxies and beyond. The generation of these fields via the
hydromagnetic dynamo effect involves the formation of electrical
currents by means of complex flows of conducting fluids or plasmas. At
HZDR a related experiment is under construction within the project
DRESDYN. In that experiment a precessing flow of liquid sodium will
provide the required energy for magnetic field generation.

Here we address preliminary numerical and experimental studies aimed
at the identification of parameter ranges where a dynamo can be
expected. Our kinematic dynamo models show that dynamo action is
possible just before the transition from a laminar flow state to
vigorous turbulence where the flow structure is determined by a
combination of axisymmetric and nonaxisymmetric large scale modes. By
applying the derived scaling laws, the results can be directly applied
to the parameters of the planned large device.

Keywords: Dynamo

  • Poster (Online presentation)
    MML-Workshop 2021, 22.-24.11.2021, virtuell, virtuell

Permalink: https://www.hzdr.de/publications/Publ-33446
Publ.-Id: 33446


Polyoxoplatinates as Covalently Dynamic Electron Sponges and Molecular Electronics Materials

Kondinski, A.; Ghorbani Asl, M.

Dynamic covalent chemistry is an adaptive approach that utilizes thermodynamic equilibriums towards tailoring the structural and the electronic properties of molecular assemblies. The primary application of the latter approach lies in the design of organic self-healing materials, sensors, and actuators. Herein we apply density functional theory (DFT) to explore the structural, electronic and transport properties of the [Pt₁₂O8(SO₄)₁₂]⁴⁻ cluster and its derivatives. The cluster is a polyoxometalate (POM) that exhibits six {O−Pt−Pt−O} moieties. The latter moieties are redox responsive and covalently dynamic, allowing the POM to store up to twelve electrons. In our proposed Au/POM/Au junction, the simulations show that the electron conduction strongly depends on the redox of POM but more weakly on its rotations with respect to the Au surface. Moreover, the POM shows promising spin-polarized current behaviour, which can be modulated using bias and gate voltages.

Keywords: polyoxometalates (POMs); platinum; computational modelling; DFT; charge storage; molecular electronics

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Permalink: https://www.hzdr.de/publications/Publ-33445
Publ.-Id: 33445


Resonant SAXS data used in publication: "Probing ultrafast laser plasma processes inside solids with resonant small angle X-ray scattering"

Gaus, L.; Bischoff, L.; Bussmann, M.; Cunningham, E.; Curry, C. B.; E, Juncheng; Galtier, E.; Gauthier, M.; Laso García, A.; Garten, M.; Glenzer, S.; Grenzer, J.; Gutt, C.; Hartley, N.; Huang, L.; Hübner, U.; Kraus, D.; Lee, H. J.; McBride, E. E.; Metzkes-Ng, J.; Nagler, B.; Nakatsutsumi, M.; Nikl, J.; Ota, M.; Pelka, A.; Prencipe, I.; Randolph, L.; Rödel, M.; Sakawa, Y.; Schlenvoigt, H.-P.; Smid, M.; Treffert, F.; Voigt, K.; Zeil, K.; Cowan, T.; Schramm, U.; Kluge, T.

Resonant Small-angle x-ray scattering raw data obtained in measurements at MEC at LCLS and evalutation of the asymmetry in the scattering patterns. The data set is structured in case 1/Si-Cu-compound targets and case 2/Cu-only-targets as presented in the publication for on- and off-resonant XFEL probe energies.

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Permalink: https://www.hzdr.de/publications/Publ-33444
Publ.-Id: 33444


Dynamo action of the large scale flow in a precessing cylinder

Giesecke, A.; Pizzi, F.; Stefani, F.

Precession is a well known phenomenon that (in a very general sense) paraphrases the
temporal change of the orientation of the spin axis of rotating objects. In rotating celestial bodies
with liquid interior precession causes a volume force that directly drives a non-axisymmetric fluid
flow [1]. Paradigmatic example is the liquid core of the Earth [2], for which the forcing is
considerably strong due to the rather large angle between rotation axis and precession axis. An even
stronger forcing is assumed for the ancient moon three to four billion years ago [3]. Precessional
forcing of the fluid interior of planets or moons is of interest because the resulting internal flows in
terms of inertial modes or turbulence back-react on the rotation of the whole body, which may
become evident for example in length of day variations or periodic changes of the nutation angle.
Furthermore a precession-driven flow of an electrically conductive fluid is capable of generating a
large scale magnetic field [4]. From an energetic point of view, the directly driven non-
axissymmetric flow is not sufficient to generate a magnetic field [5], however, multifaceted
instabilities of the primary flow provide the possibility to extract a large a amount of kinetic energy
from the rotational fluid motions into a fluid flow, which may be more suitable of generating a
magnetic field via electromagnetic induction [6].
In order to investigate to what extent a precession-driven flow can power a dynamo, and what
properties the related magnetic field would have, an experiment is currently being constructed at
HZDR, in which 6 tons of liquid sodium will precess in a cylinder with 2 meters height and 2
meters in diameter [7]. The design of the experiment is attended by comprehensive numerical
simulations, which showed that at the edge of the transition between a complex but still laminar
flow to a fully developed turbulent state, onset of dynamo action can be expected [8]. This state of
flow is characterized by an almost complete transformation of the original rotation into large-scale
inertial waves and small-scale turbulent flow. The dynamo effect found in the simulations is mainly
due to an evolving axially symmetric flow component and the strong shear layer near the outer
walls due to the massive extraction of rotational energy [9]. Free inertial waves in the form of
triadic resonances as the first instability, which describe the transition from the stationary to the
time-dependent state, do not seem to play any special role for the dynamo-effect. Open questions
concern the role of this triadic instability as a trigger for the transition to turbulence, the character of
the turbulence itself (is it three-dimensional or quasi-geostrophic) and the very mechanism that
causes the redistribution of the internal angular momentum and/or torque that goes along with the
significant modification of the large scale pattern of the velocity field.

1.
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Stewartson & Roberts 1963, J. Fluid Mech. 17 (1), 1-20.
Malkus 1968, Science, 160, 259
Cebron et al. 2019, Geophys. J. Int., 219 (1), 34-57
Tilgner 2005, Phys. Fluids, 17, 034104
Loper 1975, Phys. Earth Planet. Inter. 11 (1), 43-60
Kerswell 1999, J. Fluid Mech. 382, 283-306
Stefani et al. 2015, Magnetohydrodynamics, 51 (2), 275-284
Giesecke et al. 2018, Phys. Rev. Lett. 120, 024502
Giesecke et al. 2018, Geophys. Astrophys. Fluid Mech., 113 (1-2), 235-255

Keywords: Dynamo

  • Invited lecture (Conferences)
    IV Russian Conference on Magnetohydrodynamics, 20.-22.09.2021, Perm, Russland

Permalink: https://www.hzdr.de/publications/Publ-33443
Publ.-Id: 33443


Rational Linker Design to Accelerate Excretion and Reduce Background Uptake of Peptidomimetic PSMA-Targeting Hybrid Molecules.

Eder, A.; Schäfer, M.; Schmidt, J.; Bauder-Wüst, U.; Roscher, M.; Leotta, K.; Haberkorn, U.; Kopka, K.; Eder, M.

The evolution of peptidomimetic hybrid molecules for preoperative imaging and guided surgery targeting the prostate-specific membrane antigen (PSMA) significantly progressed over the past few years, and some approaches are currently being evaluated for further clinical translation. However, accumulation in nonmalignant tissue such as kidney, bladder, spleen, or liver might limit tumor-to-background contrast for precise lesion delineation, particularly in a surgical setting. To overcome these limitations, a rational linker design aims at the development of a second generation of PSMA-11-based hybrid molecules with an enhanced pharmacokinetic profile and improved imaging contrast. Methods: A selection of rationally designed linkers was introduced to the PSMA-targeting hybrid molecule Glu-urea-Lys-HBED-CC-IRDye800CW, resulting in a second-generation peptidomimetic hybrid molecule library. The biologic properties were investigated in cell-based assays. In a preclinical proof-of-concept study with the radionuclide 68Ga, the impact of the modifications was evaluated by determination of specific tumor uptake, pharmacokinetics, and fluorescence imaging in tumor-bearing mice. Results: The modified hybrid molecules carrying various selected linkers revealed high PSMA-specific binding affinity and effective internalization. The highest tumor-to-background contrast of all modifications investigated was identified for the introduction of a histidine- (H) and glutamic acid (E)-containing linker ((HE)3-linker) between the PSMA-binding motif and the chelator. In comparison to the parental core structure, uptake in nonmalignant tissue was significantly reduced to a minimum, as exemplified by an 11-fold reduced spleen uptake from 38.12 ± 14.62 percentage injected dose (%ID)/g to 3.47 ± 1.39 %ID/g (1 h after injection). The specific tumor uptake of this compound (7.59 ± 0.95 %ID/g, 1 h after injection) was detected to be significantly higher than that of the parental tracer PSMA-11. These findings confirmed by PET and fluorescence imaging are accompanied by an enhanced pharmacokinetic profile with accelerated background clearance at early time points after injection. Conclusion: The novel generation of PSMA-targeting hybrid molecules reveals fast elimination, reduced background organ enrichment, and high PSMA-specific tumor uptake meeting the key demands for potent tracers in nuclear medicine and fluorescence-guided surgery. The approach's efficacy in improving the pharmacokinetic profile highlights the strengths of rational linker design as a powerful tool in strategic hybrid-molecule development.

Keywords: PSMA; guided surgery; hybrid molecules; pharmacokinetic profile; prostate cancer

Permalink: https://www.hzdr.de/publications/Publ-33442
Publ.-Id: 33442


Spectroscopic and modeling study of the sorption of Ln³⁺ (Eu) and An³⁺ (Am, Cm) on Ca-feldspars

Lessing, J.; Neumann, J.; Bezzina, J. P.; Bok, F.; Lützenkirchen, J.; Brendler, V.; Stumpf, T.; Schmidt, M.

INTRODUCTION
Deep geological repositories are considered as a safe disposal strategy for radioactive waste due their ability to isolate toxic components from the biosphere over hundreds of thousands of years. Minor actinides and Pu dominate the radiotoxicity of spent nuclear fuel over these long time scales. Due to the expected reducing conditions in the underground repository, the trivalent oxidation state is dominant for Am and Cm, and will also be relevant for Pu. For investigations of the mobility of the trivalent actinides Am(III) and Cm(III), the less toxic trivalent rare earth elements, in particular Eu(III), are commonly used.
In Germany and many other countries, crystalline rock is being considered as a possible host rock. Therefore, there is a need for understanding the sorption behavior of radionuclides on this material. Crystalline rock (e.g. granite), consists mainly of quartz, feldspars, and mica. Recently, the retention of trivalent actinides by K-feldspar was investigated from a thermodynamic and structural point of view.[1] Here, we extend this study towards Ca-feldspars (plagioclases), which may show a different sorption behavior due to their different elemental composition, crystal structure, and surface charge behavior.
DESCRIPTION OF THE WORK
Synthetic Ca-feldspar and natural plagioclases of different Ca amounts were used for zeta potential measurements and batch sorption experiments under different geochemical conditions ([M³⁺] = 52 nM – 10 μM; solid-liquid ratio = 1 – 3 g/L, I = 0,1 M NaCl, pH = 3 – 9) to quantify the uptake of Am(III) and Eu(III). For analysis of the sorption structure of trivalent f-elements on the molecular level, time-resolved laser-induced spectroscopy (TRLFS) using Cm(III) as a luminescent probe was carried out on synthetic Ca-feldspar. The obtained data were used to develop a surface complexation model (SCM) and to derive surface complexation parameters for the spectroscopically identified surface complexes.
RESULTS AND DISCUSSION
Zeta potential investigations of all Ca-feldspars show a decrease of the potential for pH = 2 – 4 due to surface site deprotonation. In contrast to the previously reported trend for K-feldspar, the zeta potential increases for pH = 4 – 7, with a stronger increase with higher Ca²⁺ concentration in the crystal lattice of the investigated plagioclases, even reaching positive values in the case of the synthetic Ca-feldspar. This effect can be traced to dissolved Al³⁺: Due to differences in solubility, Al³⁺ concentration in solution increases with increasing Ca²⁺ in the crystal lattice. Experiments on K-feldspar with added Al³⁺ reveal a connection between its concentration and the increase of the zeta potential.
All observed Ca-feldspars show a strong sorption uptake of trivalent f-elements for pH > 6. K- and Ca-feldspars seem to have a similar sorption behavior for low [M³⁺].[1] In contrast, Ca-feldspar has a slightly stronger sorption affinity when the metal concentrations is increased. This leads to a steeper sorption edge with increasing Ca²⁺ concentration in the crystal lattice of the mineral.
Spectroscopic studies with Cm(III) on synthetic Ca-feldspar reveal three sorption complexes: one inner sphere complex (IS) and its two hydrolysis forms, which have the same band positions as previously determined for K-feldspar.[1] Therefore, it can be concluded that the structure of the formed IS complexes is independent on the feldspar type. Differences are only observed for the quantitative contributions of the surface complexes. In particular, hydrolysis of the IS complex is stronger in the case of the Ca-feldspar.
Batch sorption data and the information about spectroscopically identified surface complexes were then combined to develop a SCM for Ca-feldspar that describes the experimental data. The formation constants of the surface complexes were determined to be −8.37; −10.81, and −16.35, respectively and are very similar to those of the K-feldspar.[1]
From the applied multi-method approach, we conclude that the sorption of trivalent f-elements on K- and Ca-feldspar is most likely comparable for relevant, natural conditions. Therefore, it may be possible not to distinguish between the two minerals in reactive transport simulations, which will reduce calculation resources needed for a reliable risk assessment of repositories for radioactive waste.
REFERENCES
[1] J. Neumann et al., “A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar,” Journal of Colloid Interface Science, vol. 591, pp. 490–499 (2021)
[2] Neumann and Lessing et al., “Structural and modeling study of the retention of trivalent f-elements (Am, Cm, Eu) by natural and synthetic Ca-feldspars”, in preparation.

Keywords: Sorption; Trivalent metal ions; Actinides; Ca-feldspar; Surface complexation model; TRLFS; Zeta potential

  • Poster
    TransRet2020, 12.-13.10.2021, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33441
Publ.-Id: 33441


The disappearance and return of nanoparticles upon low energy ion irradiation

Choupanian, S.; Nagel, A.; Möller, W.; Pacholski, C.; Ronning, C.

Ion irradiation of bulk and thin film materials is tightly connected to well described effects such as sputtering or/and ion beam mixing. However, when a nanoparticle is ion irradiated and the ion range is comparable to the nanoparticle size, these effects are to be reconsidered essentially. This study investigates the morphology changes of silver nanoparticles on top of silicon substrates, being irradiated with Ga+ ions in an energy range from 1 to 30 keV. The hemispherical shaped nanoparticles become conical due to an enhanced and curvature-dependent sputtering, before they finally disappear. The sputter yield and morphology changes can be well described by 3D Monte Carlo TRI3DYN simulations. However, the combination of sputtering, ion beam mixing, ion beam induced diffusion, and Ostwald ripening at ion energies lower than 8 keV results in the reappearance of new particles. These newly formed nanoparticles appear in various structures depending on the material and ion energy

Keywords: Ag nanoparticles; Ion beam mixing; Ion-nanoparticle interaction; Ostwald ripening; Phase sepereation

Permalink: https://www.hzdr.de/publications/Publ-33440
Publ.-Id: 33440


Deterministic Shallow Dopant Implantation in Silicon with Detection Confidence Upper-Bound to 99.85% by Ion–Solid Interactions

Jakob, A. M.; Robson, S. G.; Schmitt, V.; Mourik, V.; Posselt, M.; Spemann, D.; Johnson, B. C.; Firgau, H. R.; Mayes, E.; McCallum, J. C.; Morello, A.; Jamieson, D. N.

Silicon chips containing arrays of single dopant atoms can be the material of choice for classical and quantum devices that exploit single donor spins. For example, group-V donors implanted in isotopically purified 28Si crystals are attractive for large-scale quantum computers. Useful attributes include long nuclear and electron spin lifetimes of 31P, hyperfine clock transitions in 209Bi or electrically controllable 123Sb nuclear spins. Promising architectures require the ability to fabricate arrays of individual near-surface dopant atoms with high yield. Here, an on-chip detector electrode system with 70 eV root-mean-square noise (≈20 electrons) is employed to demonstrate near-room-temperature implantation of single 14 keV 31P+ ions. The physics model for the ion–solid interaction shows an unprecedented upper-bound single-ion-detection confidence of 99.85 ± 0.02% for near-surface implants. As a result, the practical controlled silicon doping yield is limited by materials engineering factors including surface gate oxides in which detected ions may stop. For a device with 6 nm gate oxide and 14 keV 31P+ implants, a yield limit of 98.1% is demonstrated. Thinner gate oxides allow this limit to converge to the upper-bound. Deterministic single-ion implantation can therefore be a viable materials engineering strategy for scalable dopant architectures in silicon devices.

Keywords: Deterministic single-ion implantation; Near-surface dopant location; Quantum computers; Ion Beam Induced Charge Collection

Permalink: https://www.hzdr.de/publications/Publ-33439
Publ.-Id: 33439


Investigation of a buoyancy-driven instability during horizontal miscible displacement*

Stergiou, G.; Dezso, H.; Eckert, K.; Schwarzenberger, K.

Hydrodynamic instabilities in miscible reactive systems have significant impact on applications such as: CO2 sequestration, soil reparation, or particle formation in precipitation systems. A buoyancy-induced instability has been observed when a fluid horizontally displaces another miscible fluid of different density, resulting in a complex flow field. With this study, we intended to characterize the flow patterns in such systems and to investigate their dependence on parameters such as the injection flow rate and the fluids density difference. We performed reactive and non-reactive experiments in a microscale geometry and explored the intricate 3D flow conditions of the system, using micro-Particle Image Velocimetry. The results evidence the existence of flow structures present in equivalent numerical studies and reveal the dependency of the instability on the direction of the displacement.

*Funded by the German Aerospace Center (DLR) provided by BMWi, Grant No. 50WM2061.

  • Lecture (Conference)
    74th APS Division of Fluid Dynamics Meeting, 21.-23.11.2021, Phoenix, USA

Permalink: https://www.hzdr.de/publications/Publ-33438
Publ.-Id: 33438


Atomic layer etching of SiGe nanowires

Khan, M. B.; Shakeel, S.; Richter, K.; Ghosh, S.; Deb, D.; Hübner, R.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

Developments in the fabrication techniques like lithography, etching, thin-film deposition, and metallization, etc. have enhanced device the performance of the complementary metal-oxide-semiconductor (CMOS) transistors mainly by the scaling-down. Innovative concepts need to be incorporated to further improve the device performance as the scaling limits are being reached.
We report on the development of the atomic layer etching (ALE) process to fabricate smooth SiGe-on-insulator (SiGeOI) nanowire using the conventional dry etching tool. First, nano-patterns were made on SiGeOI samples using electron beam lithography. Then these patterns were transferred into the SiGeOI layer using an inductively coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, the ALE process was developed to smoothen the nanowire and to reduce their widths. For the surface modification step, SF6 was used, while Ar+ was used for the subsequent modified layer removal step. The ALE cycle sequence was: modification with 60 sccm SF6 for 20 s, 60 sccm Ar purge for 15 s, layer removal with 60 sccm Ar for 10 s using 25 W platen power, and 40 sccm Ar purge for 10 s.
Various ALE cycles were performed to investigate the effect of ALE on the nanowire roughness and width. The surface of etched features was studied using the atomic force microscopy (AFM) (figure 1 (a)). A reduction in the width of the wire was seen with the increasing number of the ALE cycles. Figure 1 (b) shows the root mean square (r.m.s) surface roughness of the buried oxide after certain numbers of the ALE cycles. The roughness went down from ca. 6 nm to 1 nm or below (exact value could not be calculated due to limitation of the AFM tip) as the number of ALE cycles was increased from 78 to 102.
Figure 2 shows sub-12 nm nanowires with smooth sidewalls fabricated after performing 63 ALE cycles. An etch per cycle of 1.1 Å was attained. This process, developed on a conventional ICP-RIE tool, can be used to further scale down the nanowires.

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  • Poster (Online presentation)
    Micro and Nano Engineering Conference, 2021, 20.-23.09.2021, Turin, Italy

Permalink: https://www.hzdr.de/publications/Publ-33437
Publ.-Id: 33437


Controlled Silicidation of Silicon Nanowires using Flash Lamp Annealing

Khan, M. B.; Prucnal, S.; Ghosh, S.; Deb, D.; Hübner, R.; Pohl, D.; Rebohle, L.; Mikolajick, T.; Erbe, A.; Georgiev, Y.

Among other new device concepts, nickel silicide (NiSix)-based Schottky barrier nanowire transistors are projected to supplement down-scaling of the complementary metal-oxide-semiconductor (CMOS) technology as its physical limits are reached. Control over the NiSix phase and its intrusions into the nanowire are essential for superior performance and down-scaling of these devices. Several works have shown control over the phase, but control over the intrusion lengths has remained a challenge. To overcome this, we report a novel millisecond-range flash-lamp-annealing (FLA)-based silicidation process. Nanowires are fabricated on silicon-on-insulator substrates using a top-down approach. Subsequently, Ni silicidation experiments are carried out using FLA. It is demonstrated that this silicidation process gives unprecedented control over the silicide intrusions. Scanning electron microscopy and high-resolution transmission electron microscopy are performed for structural characterization of the silicide. FLA temperatures are estimated with the help of simulations.

Related publications

Permalink: https://www.hzdr.de/publications/Publ-33436
Publ.-Id: 33436


Stable acceleration of intense proton beams to energies beyond 80 MeV at rep-rated laser systems

Ziegler, T.; Bernert, C.; Bock, S.; Brack, F.-E.; Cowan, T.; Dover, N. P.; Garten, M.; Gaus, L.; Göthel, I.; Kiriyama, H.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Nishiuchi, M.; Püschel, T.; Rehwald, M.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

We report on experimental investigations of proton acceleration from laser-irradiated solid foils with the Draco-PW laser, where highest proton cut-off energies were achieved for temporal pulse parameters that varied significantlyfrom those of an ideally Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal shape ofthe last picoseconds around the main pulse and to study the effect on proton acceleration from thin foil targets. The results show that short and asymmetric pulses generated by positive third order dispersion values are favourable for proton acceleration and can lead to maximum energies above 60 MeV at 18 J laser energy for thin plastic foils, effectively doubling the maximum energy compared to ideally compressed FTL pulses. This performance optimization was the key to perform worlds first dose-controlled in-vivo studies with laser accelerated protons.

The talk will further report on experiments we have carried out in the relativistically induced transparancy regime where the target turns transparent during the laser pulse interaction. We show recent data how the experimental signatures of the accelerated protons in this regime change compared to standard TNSA conditions and how we could reproduce those results at another similar laser laser system.

  • Invited lecture (Conferences)
    5th European Advanced Accelerator Concepts Workshop, 20.-23.09.2021, Rome, Italy

Permalink: https://www.hzdr.de/publications/Publ-33435
Publ.-Id: 33435


Assessment of the validity of a log-law for wall-bounded turbulent bubbly flows

Bragg, A.; Liao, Y.; Fröhlich, J.; Ma, T.

There has been considerable discussion in recent years concerning whether a log-law exists for wall-bounded,
turbulent bubbly flows. Previous studies have argued for the existence of such a log-law, with a modified von
K´arm´an constant, and this is used in various modelling studies. We provide a critique of this idea, and present
several theoretical reasons why a log-law need not be expected in general for wall-bounded, turbulent bubbly
flows. We then demonstrate using recent data from interface-resolving Direct Numerical Simulations that when
the bubbles make a significant contribution to the channel flow dynamics, the mean flow profile of the fluid can
deviate significantly from the log-law behaviour that approximately holds for the single-phase case. The departures
are not surprising and the basic reason for them is simple, namely that for bubbly flows, the mean flow is
affected by a number of additional dynamical parameters, such as the void fraction, that do not play a role for the
single-phase case. As a result, the inner/outer asymptotic regimes that form the basis of the derivation of the loglaw
for single-phase flow do not exist in general for bubbly turbulent flows. Nevertheless, we do find that for
some cases, the bubbles do not cause significant departures from the unladen log-law behaviour. Moreover, we
show that if departures occur these cannot be understood simply in terms of the averaged void fraction, but that
more subtle effects such as the bubble Reynolds number and the competition between the wall-induced turbulence
and the bubble-induced turbulence must play a role.

Keywords: Bubbly flow; Log-law; Wall-bounded turbulent flows

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Permalink: https://www.hzdr.de/publications/Publ-33434
Publ.-Id: 33434


Origin and avoidance of double peaks in the induced voltage of a thermomagnetic generator for harvesting low-grade waste heat

Dzekan, D.; Kischnik, T. D.; Diestel, A.; Kornelius, N.; Fähler, S.

Thermomagnetic harvesting is an emerging approach to convert low-grade
waste heat to electricity, which recently obtained a boost due to the development of both,
more efficient functional materials and innovative device concepts. Here we examine a
thermomagnetic generator which utilizes Gadolinium as thermomagnetic material and report
on double peaks of the induced voltage. By a combination of experiments and theory we
show that these double peaks originate from the interaction of an asymmetric magnetization
curve and a pretzel like magnetic field topology. Double peaks are detrimental for the output
power and can be avoided by matching the magnetization change by adjusting cold and hot
fluid flow.

Keywords: Thermomagnetic Energy Harvesting; Thermomagnetic Generator; Magnetocaloric Refrigeration; Magnetic Materials

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Permalink: https://www.hzdr.de/publications/Publ-33433
Publ.-Id: 33433


A Machine-Learning Surrogate Model for ab initio Electronic Correlations at Extreme Conditions

Dornheim, T.; Moldabekov, Z.; Cangi, A.

The electronic structure in matter under extreme conditions is a challenging complex system prevalent in astrophysical objects and highly relevant for technological applications. We show how machine-learning surrogates in terms of neural networks have a profound impact on the efficient modeling of matter under extreme conditions. We demonstrate the utility of a surrogate model that is trained on \emph{ab initio} quantum Monte Carlo data for various applications in the emerging field of warm dense matter research.

Keywords: Machine Learning; Surrogate model; warm dense matter

Permalink: https://www.hzdr.de/publications/Publ-33432
Publ.-Id: 33432


Fermion Sign Problem in Path Integral Monte Carlo Simulations: Grand-canonical ensemble

Dornheim, T.

We present a practical analysis of the fermion sign problem in fermionic path integral Monte Carlo (PIMC) simulations in the grand-canonical ensemble (GCE). As a representative model system, we consider electrons in a harmonic trap. We find that the sign problem in the GCE is even more severe than in the canonical ensemble at the same conditions, which, in general, makes the latter the preferred option. Despite these difficulties, we show that fermionic PIMC simulations in the GCE are still feasible in many cases, which potentially gives access to important quantities like the compressiblity or the Matsubara Greens function. This has important implications for contemporary fields of research such as warm dense matter, ultracold atoms, and electrons in quantum dots.

Keywords: path integral Monte Carlo; Fermion sign problem

Permalink: https://www.hzdr.de/publications/Publ-33431
Publ.-Id: 33431


Ab initio path integral Monte Carlo approach to the momentum distribution of the uniform electron gas at finite temperature without fixed nodes

Dornheim, T.; Böhme, M.; Militzer, B.; Vorberger, J.

We present extensive new ab initio path integral Monte Carlo results for the momentum distribution function n(k) of the uniform electron gas in the warm dense matter regime over a broad range of densities and temperatures. This allows us to study the nontrivial exchange-correlation-induced increase of low-momentum states around the Fermi temperature, and to investigate its connection to the related lowering of the kinetic energy compared to the ideal Fermi gas. In addition, we investigate the impact of quantum statistics on both n(k) and the off-diagonal density matrix in coordinate space, and find that it cannot be neglected even in the strongly coupled electron liquid regime. Our results were derived without any nodal constraints, and thus constitute a benchmark for other methods and approximations.

Keywords: path integral Monte Carlo; uniform electron gas; momentum distribution; warm dense matter

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Permalink: https://www.hzdr.de/publications/Publ-33430
Publ.-Id: 33430


Momentum distribution of the Uniform Electron Gas at finite temperature: Effects of spin-polarization

Dornheim, T.; Vorberger, J.; Militzer, B.; Moldabekov, Z.

We carry out extensive direct path integral Monte Carlo (PIMC) simulations of the uniform electron gas (UEG) at finite temperature for different values of the spin-polarization ξ. This allows us to unambiguously quantify the impact of spin-effects on the momentum distribution function n(k) and related properties. We find that interesting physical effects like the interaction-induced increase in the occupation of the zero-momentum state n(0) substantially depend on ξ. Our results further advance the current understanding of the UEG as a fundamental model system, and are of practical relevance for the description of transport properties of warm dense matter in an external magnetic field.
All PIMC results are freely available online and can be used as a benchmark for the development of new methods and applications.

Keywords: path integral Monte Carlo; uniform electron gas; momentum distribution; spin-effects; warm dense matter

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Permalink: https://www.hzdr.de/publications/Publ-33429
Publ.-Id: 33429


Nonlinear density response from imaginary-time correlation functions: Ab initio path integral Monte Carlo simulations of the warm dense electron gas

Dornheim, T.; Moldabekov, Z.; Vorberger, J.

The \emph{ab initio} path integral Monte Carlo (PIMC) approach is one of the most successful methods in quantum many-body theory. A particular strength of this method is its straightforward access to imaginary-time correlation functions (ITCF). For example, the well-known density-density ITCF F(q,τ) allows one to estimate the linear response of a given system for all wave vectors q from a single simulation of the unperturbed system. Moreover, it constitutes the basis for the reconstruction of the dynamic structure factor S(q,ω) -- a key quantity in state-of-the-art scattering experiments. In this work, we present analogous relations between the nonlinear density response in quadratic and cubic order of the perturbation strength and generalized ITCFs measuring correlations between up to four imaginary-time arguments. As a practical demonstration of our new approach, we carry out simulations of the warm dense electron gas and find excellent agreement with previous PIMC results that had been obtained with substantially larger computational effort. In addition, we give a relation between a cubic ITCF and the triple dynamic structure factor S(q1,ω1;q2,ω2), which evokes the enticing possibility to study dynamic three-body effects on an \emph{ab initio} level.

Keywords: Nonlinear response; path integral Monte Carlo; imaginary-time correlation functions

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Permalink: https://www.hzdr.de/publications/Publ-33428
Publ.-Id: 33428


Nonlinear electronic density response of the ferromagnetic uniform electron gas at warm dense matter conditions

Dornheim, T.; Moldabekov, Z.; Vorberger, J.

In a recent Letter [T.~Dornheim \emph{et al.}, Phys.~Rev.~Lett.~\textbf{125}, 085001 (2020)], we have presented the first \emph{ab initio} results for the nonlinear density response of electrons in the warm dense matter regime. In the present work, we extend these efforts by carrying out extensive new path integral Monte Carlo (PIMC) simulations of a \emph{ferromagnetic} electron gas that is subject to an external harmonic perturbation. This allows us to unambiguously quantify the impact of spin-effects on the nonlinear density response of the warm dense electron gas. In addition to their utility for the description of warm dense matter in an external magnetic field, our results further advance our current understanding of the uniform electron gas as a fundamental model system, which is important in its own right.

Keywords: Nonlinear response; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33427
Publ.-Id: 33427


Classical bridge functions in classical and quantum plasma liquids

Lucco Castello, F.; Tolias, P.; Dornheim, T.

Bridge functions, the missing link in the exact description of strong correlations, are indirectly extracted from specially designed molecular dynamics simulations of classical one-component plasma liquids and accurately parameterized. Their incorporation into an advanced integral equation theory description of Yukawa one-component plasma liquids and a novel dielectric formalism scheme for quantum one-component plasma liquids leads to an unprecedented agreement with available molecular dynamics simulations and new ab initio path integral Monte Carlo simulations, respectively.

Keywords: Dielectric theory; Bridge functions; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33426
Publ.-Id: 33426


Path integral Monte Carlo approach to the structural properties and collective excitations of liquid 3He without fixed nodes

Dornheim, T.; Moldabekov, Z.; Vorberger, J.; Militzer, B.

Due to its nature as a strongly correlated quantum liquid, ultracold helium is characterized by the nontrivial interplay of different physical effects. Bosonic 4He exhibits superfluidity and Bose-Einstein condensation. Its physical properties have been accurately determined on the basis of ab initio path integral Monte Carlo (PIMC) simulations. In contrast, the corresponding theoretical description of fermionic 3He is severely hampered by the notorious fermion sign problem, and previous PIMC results have been derived by introducing the uncontrolled fixed-node approximation. In this work, we present extensive new PIMC simulations of normal liquid 3He without any nodal constraints. This allows us to to unambiguously quantify the impact of Fermi statistics and to study the effects of temperature on different physical properties like the static structure factor S(q) , the momentum distribution n(q) , and the static density response function χ(q). In addition, the dynamic structure factor S(q, ω) is rigorously reconstructed from imaginary-time PIMC data. From simulations of 3He , we derived the familiar phonon–maxon–roton dispersion function that is well-known for 4He and has been reported previously for two-dimensional 3He films (Nature 483:576–579 (2012)). The comparison of our new results for both S(q) and S(q, ω) with neutron scattering measurements reveals an excellent agreement between theory and experiment.

Keywords: path integral Monte Carlo; Helium; ultracold atoms

Permalink: https://www.hzdr.de/publications/Publ-33425
Publ.-Id: 33425


Nonlinear interaction of external perturbations in Warm Dense Matter

Dornheim, T.; Vorberger, J.; Moldabekov, Z.; Bonitz, M.

We present extensive new ab initio path integral Monte Carlo (PIMC) results for an electron gas at warm dense matter conditions that is subject to multiple harmonic perturbations. In addition to the previously investigated nonlinear effects at the original wave number [Dornheim \emph{et al.}, PRL \textbf{125}, 085001 (2020)] and the excitation of higher harmonics [Dornheim \emph{et al.}, PRR \textbf{3}, 033231 (2021)], the presence of multiple external potentials leads to mode-coupling effects, which constitute the dominant nonlinear effect and lead to a substantially more complicated density response compared to linear response theory. One possibility to estimate mode-coupling effects from a PIMC simulation of the unperturbed system is given in terms of generalized imaginary-time correlation functions that have been recently introduced by Dornheim \emph{et al.}~[JCP \textbf{155}, 054110 (2021)]. In addition, we extend our previous analytical theory of the nonlinear density response of the electron gas in terms of the static local field correction [Dornheim \emph{et al.}, PRL \textbf{125}, 235001 (2020)], which allows for a highly accurate description of the PIMC results with negligible computational cost.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo; mode coupling

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Permalink: https://www.hzdr.de/publications/Publ-33424
Publ.-Id: 33424


Nonlinear Density Response and Higher Order Correlation Functions in Warm Dense Matter

Dornheim, T.; Vorberger, J.; Moldabekov, Z.

In a recent letter [Phys. Rev. Lett. 125, 085001 (2020)], Dornheim et al. have presented the first ab initio path integral Monte Carlo (PIMC) results for the nonlinear electronic density response at warm dense matter (WDM) conditions. In the present work, we extend these considerations by exploring the relation between the nonlinear response and three-/four-body correlation functions from many-body theory. In particular, this connection directly implies a comparably increased sensitivity of the nonlinear response to electronic exchange–correlation (XC) effects, which is indeed confirmed by our analysis over the entire relevant range of densities (rs=0.5,…,10) and temperatures (θ=0.01,…,4). Finally, our work suggests the possibility of deliberately probing the nonlinear regime to experimentally probe three- and potentially even four-body correlation functions in WDM.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo

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Permalink: https://www.hzdr.de/publications/Publ-33423
Publ.-Id: 33423


Integral equation theory based dielectric scheme for strongly coupled electron liquids

Tolias, P.; Lucco Castello, F.; Dornheim, T.

In a recent paper, Lucco Castello et al. (arXiv:2107.03537) provided an accurate parameterization of classical one-component plasma bridge functions that was embedded in a novel dielectric scheme for strongly coupled electron liquids. Here, this approach is rigorously formulated, its set of equations is formally derived, and its numerical algorithm is scrutinized. A systematic comparison with available and new path integral Monte Carlo simulations reveals a rather unprecedented agreement especially in terms of the interaction energy and the long wavelength limit of the static local field correction.

Keywords: Dielectric theory; linear response theory; path integral Monte Carlo

Permalink: https://www.hzdr.de/publications/Publ-33422
Publ.-Id: 33422


Density response of the warm dense electron gas beyond linear response theory: Excitation of harmonics

Dornheim, T.; Böhme, M.; Moldabekov, Z.; Vorberger, J.; Bonitz, M.

In a recent letter, Dornheim et al. [Phys. Rev. Lett. 125, 085001 (2020)] have investigated the nonlinear density response of the uniform electron gas in the warm dense matter regime. More specifically, they have studied the cubic response function at the first harmonic, which cannot be neglected in many situations of experimental relevance. In this paper, we go one step further and study the full spectrum of excitations at the higher harmonics of the original perturbation based on extensive new ab initio path integral Monte Carlo (PIMC) simulations. We find that the dominant contribution to the density response beyond linear response theory is given by the quadratic response function at the second harmonic in the moderately nonlinear regime. Furthermore, we show that the nonlinear density response is highly sensitive to exchange-correlation effects, which makes it a potentially valuable tool of diagnostics. To this end, we present a theoretical description of the nonlinear electronic density response based on the recent effective static approximation to the local field correction [T. Dornheim et al., Phys. Rev. Lett. 125, 235001 (2020)], which accurately reproduces our PIMC data with negligible computational cost.

Keywords: Nonlinear response; warm dense matter; path integral Monte Carlo

Permalink: https://www.hzdr.de/publications/Publ-33421
Publ.-Id: 33421


Robust formation of nanoscale magnetic skyrmions in easy-plane anisotropy thin film multilayers with low damping

Flacke, L.; Ahrens, V.; Mendisch, S.; Körber, L.; Böttcher, T.; Meidinger, E.; Yaqoob, M.; Müller, M.; Liensberger, L.; Kakay, A.; Becherer, M.; Pirro, P.; Althammer, M.; Geprägs, S.; Huebl, H.; Gross, R.; Weiler, M.

We experimentally demonstrate the formation of room-temperature skyrmions with radii of about 25 nm in easy-plane anisotropy multilayers with an interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of individual magnetic skyrmions by magnetic force microscopy and find that the skyrmions are stable in out-of-plane fields up to about 200 mT. We determine the interlayer exchange coupling as well as the strength of the interfacial DMI. Additionally, we investigate the dynamic microwave spin excitations by broadband
magnetic resonance spectroscopy. From the uniform Kittel mode we determine the magnetic anisotropy and lowdamping α < 0.04. We also find clear magnetic resonance signatures in the nonuniform (skyrmion) state. Our findings demonstrate that skyrmions in easy-plane multilayers are promising for spin-dynamical applications.

Keywords: skyrmion; ferromagnetic resonance; DMI; low damping

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Permalink: https://www.hzdr.de/publications/Publ-33420
Publ.-Id: 33420


Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Weiner, J.; Roth, L.; Kranz, M.; Brust, P.; Boelen, A.; Klöting, N.; Heiker, J. T.; Blüher, M.; Tönjes, A.; Pfluger, P. T.; Stumvoll, M.; Mittag, J.; Krause, K.

Objective: Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of bodytemperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms. Methods: Distinct
thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis. Results: In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice. Conclusion: This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

Keywords: Beige adipose tissue; Brown adipose tissue; Leptin; Thermogenesis; Thyroid hormone; White adipose tissue browning

Permalink: https://www.hzdr.de/publications/Publ-33417
Publ.-Id: 33417


Data publication: Uptake of niobium by cement systems relevant for nuclear waste disposal: impact of ISA and chloride

Franke, K.

Daten zur Bestrahlung und Gammaspektroskopiemessung des Targets

Keywords: niobium; cyclotron; gamma spectroscopy

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Publ.-Id: 33416


High-gain quantum free-electron laser: Long-time dynamics and requirements

Kling, P.; Giese, E.; Carmesin, C. M.; Sauerbrey, R.; Schleich, W. P.

We solve the long-time dynamics of a high-gain free-electron laser in the quantum regime. In this regime each electron emits at most one photon on average, independently of the initial field. In contrast, the variance of the photon statistics shows a qualitatively different behavior for different initial states of the field. We find that the realization of a seeded quantum free-electron laser is more feasible than self-amplified spontaneous emission.

Permalink: https://www.hzdr.de/publications/Publ-33415
Publ.-Id: 33415


Zr-PAPER

Mansel, A.

Rohdaten Zr-PAPER

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Permalink: https://www.hzdr.de/publications/Publ-33414
Publ.-Id: 33414


Ghost and Gluon Propagators at Finite Temperatures within a Rainbow Truncation of Dyson–Schwinger Equations

Kaptari, L. P.; Kämpfer, B.

The finite-temperature behaviour of ghost and gluon propagators is investigated within an approach based on the rainbow truncated Dyson–Schwinger equations in Landau gauge. In Euclidean space, within the Matsubara imaginary-time formalism, the gluon propagator is not longer a O(4) symmetric function and possesses a discrete spectrum of the fourth momentum component. This leads to a different treatment of the transversal and longitudinal (with respect to the heat bath) parts of the propagator. Correspondingly, the gluon Dyson–Schwinger equation splits also into two parts. The resulting system of coupled equations is considered within the rainbow approximation and solved numerically. The solutions for the ghost and gluon propagators are obtained as a function of temperature T, Matsubara frequency Ωn and three-momentum squared k2. The effective parameters of the approach are taken from our previous fit of the corresponding Dyson–Schwinger solution to the lattice QCD data at zero temperature. It is found that, for zero Matsubara frequency, the dependence of the ghost and gluon dressing functions on k2 are not sensitive to the temperature T, while at k2 = 0 their dependence on T is quite strong. Dependence on the Matsubara frequency Ωn is investigated as well.

Permalink: https://www.hzdr.de/publications/Publ-33413
Publ.-Id: 33413


Therapy-naïve and radioresistant 3D pancreatic cancer cell cultures are effectively radiosensitized by β1 integrin targeting

Görte, J.; Danen, E.; Cordes, N.

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is one of the cancers with unmet need. The role of highly conformal radiotherapy is still under debate for PDAC. Owing to its desmoplastic nature, integrin-mediated interactions between PDAC cells and extracellular matrix (ECM) profoundly contribute to PDAC resistance. In this study, we investigated the radiochemosensitizing potential of β1 integrin targeting in therapy-naïve and radioresistant PDAC cell cultures grown in three-dimensional (3D) extracellular matrix (ECM).
Materials and Methods: In a panel of 3D, ECM based PDAC cell cultures, β1 integrin was inhibited by antibodies or siRNA-mediated knockdown. Together with X-ray irradiation and specific chemotherapies, we determined 3D colony formation capacity in therapy-naïve and radioresistant PDAC cultures. Kinome profiling, Western blotting and immunofluorescence stainings were employed to characterize these cell lines. Various siRNA screens were conducted to identify novel therapeutic targets.
Results: A significant radiosensitizing potential of β1 integrin inhibition was found both in therapy-naïve and radioresistant PDAC cell cultures. Kinome profiling upon β1 integrin targeting identified a generally declined tyrosine and serine/threonine kinase activity, which presented less prominent in radioresistant than in therapy-naïve PDAC cells. siRNA screens employing the top 34 deregulated kinases in combination with β1 integrin inhibition revealed less efficacy and less radiosensitization in radioresistant relative to therapy-naïve PDAC cell cultures. Triple inhibition of β1 integrin, protein kinase D1 (PDK1) and rearranged during transfection (RET) turned out to be most effective in reducing 3D colony formation of radioresistant PDAC cells.
Conclusion: Our study clearly shows that β1 integrins are robust targets for overcoming radioresistance in PDAC. This seems to apply equally to therapy-sensitive and radioresistant cells. Concerning tumor heterogeneity, this dual therapy-sensitizing potential might be exploitable for a significant improvement of patient survival.

Keywords: Radiotherapy; Integrins; Resistance; PDAC

Permalink: https://www.hzdr.de/publications/Publ-33412
Publ.-Id: 33412


Control of Stripe-Domain-Wall Magnetization in Multilayers Featuring Perpendicular Magnetic Anisotropy

Salikhov, R.; Samad, F.; Böhm, B.; Schneider, S.; Pohl, D.; Rellinghaus, B.; Ullrich, A.; Albrecht, M.; Lindner, J.; Kiselev, N. S.; Hellwig, O.

We report on the controlled switching of domain-wall (DW) magnetization in aligned stripe-domain
structures, stabilized in [Co(0.44 nm)/Pt(0.7 nm)]X (X = 48, 100, 150) multilayers with perpendicular
magnetic anisotropy. The switching process, induced by an external magnetic field, is monitored by measuring the evolution of the in-plane magnetization. We show that the remanent in-plane magnetization originates from the polarization of the Bloch-type DWs. With micromagnetic simulations, we reveal that
the reversal of the DW polarization is the result of the emergence and collapse of horizontal Bloch lines
within the DWs at particular strengths of the external magnetic field, applied opposite to the DW polarization. Our findings are relevant for DW-based magnonics and bubble-skyrmion applications in magnetic multilayers.

Keywords: Magnetic domains; Domain walls; Magnetization switching; Skyrmions; Spintronics; Micromagnetism

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Permalink: https://www.hzdr.de/publications/Publ-33411
Publ.-Id: 33411


Microscopic and spectroscopic investigations of uranium(VI) reduction by Desulfosporosinus hippei DSM 8344

Hilpmann, S.; Drobot, B.; Steudtner, R.; Hübner, R.; Bok, F.; Stumpf, T.; Cherkouk, A.

Clay formations are potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. Bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. For a long-term safety assessment, various aspects must be taken into account. Besides geological, geochemical, and geophysical considerations, also naturally occurring microorganisms play a crucial part in the environment of such a repository. In the event of a worst-case scenario, if water enters the disposal site, they can interact with the radionuclides and change for example the chemical speciation or the oxidation state (Lloyd et al., 2002).
Desulfosporosinus spp. are an important representative of anaerobic, sulfate-reducing microorganisms, which are present in clay formations as well as in bentonites. Various studies show that they are playing a major role in the microbial communities of these surroundings (Bagnoud et al., 2016; Matschiavelli et al., 2019). A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soil (Vatsurina et al., 2008). This bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less mobile uranium(IV).
Time-dependent reduction experiments in artificial Opalinus Clay pore water (Wersin et al., 2011) (100 µM uranium(VI), pH 5.5) showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets exhibit an increasing proportion of uranium(IV) in the cell-bound uranium. Calculations with the inclusion of extinction coefficients lead to a ratio of 39% uranium(IV) after one week. Therefore, a combined sorption-reduction process is a possible interaction mechanism.
Time-resolved laser-induced luminescence spectroscopy verifies the presence of two uranium(VI) species in the supernatant. A comparison with reference spectra leads to an assignment to a uranyl(VI) lactate and a uranyl(VI) carbonate complex. The species distribution shows a decrease of the proportion of the lactate species with time, whereas the proportion of the carbonate species remains almost constant.
Uranium aggregates are formed on the cell surface during the process, as determined by transmission electron microscopy (TEM). Furthermore, uranium occurs inside and outside the cells as well as uranium-containing vesicles.
These findings help to close existing gaps in a comprehensive safeguards concept for a repository for high-level radioactive waste in clay rock. Moreover, this study provides new insights into the interactions of sulfate-reducing microorganisms with uranium(VI).

References
Bagnoud, A., Chourey, K., Hettich, R. L., De Bruijn, I., Andersson, A. F., Leupin, O. X., Schwyn, B., and Bernier-Latmani, R.: Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock, Nat. Commun., 7, 1-10, 2016.
Lloyd, J. R. and Macaskie, L. E.: Biochemical basis of microbe-radionuclide interactions, in: Interactions of Microorganisms with Radionuclides, edited by: Keith-Roach, M. J. and Livens, F. R., Elsevier, 313-381, 2002.
Matschiavelli, N., Kluge, S., Podlech, C., Standhaft, D., Grathoff, G., Ikeda-Ohno, A., Warr, L. N., Chukharkina, A., Arnold, T., and Cherkouk, A.: The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C, Environ. Sci. Technol., 53, 10514-10524, 2019.
Vatsurina, A., Badrutdinova, D., Schumann, P., Spring, S., Vainshtein, M.: Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost, Int. J. Syst. Evol. Microbiol., 58, 1228-1232, 2008.
Wersin, P., Leupin, O. X., Mettler, S., Gaucher, E. C., Mäder, U., De Cannière, P., Vinsot, A., Gäbler, H. E., Kunimaro, T., Kiho, K., Eichinger, L.: Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland, Appl. Geochemistry, 26, 931-953, 2011.

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; Opalinus Clay

  • Poster
    Interdisziplinäres Forschungssymposium für die Sicherheit der nuklearen Entsorgung, 10.-12.11.2021, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33410
Publ.-Id: 33410


Microscopic and spectroscopic study of the uranium(VI) reduction by a sulfate-reducing microorganism

Hilpmann, S.; Steudtner, R.; Hübner, R.; Roßberg, A.; Prieur, D.; Bauters, S.; Kvashnina, K.; Stumpf, T.; Cherkouk, A.

INTRODUCTION

Clay rock is a possible host rock for the long-term storage of high-level radioactive waste and bentonites are a suitable backfill material for a final repository in clay rock and crystalline rock. For a comprehensive safety assessment of such a repository over a long period, different aspects must be taken into account. Besides intensive research regarding geological, geochemical and geophysical properties, these surroundings represent a habitat for naturally occurring microorganisms. In the event of a worst-case scenario, water can enter the repository. It is possible that microorganisms can interact with the radionuclides and thereby change the chemical speciation or the oxidation state by various processes.
Desulfosporosinus spp. play an important role as a representative of anaerobic, sulfate-reducing and spore-forming microorganisms. These bacteria occur in different clay formations as well as in bentonites.1,2 A very closely related bacterium to an isolated species from bentonite is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soils.3 Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers by different microscopic and spectroscopic techniques.

DESCRIPTION OF THE WORK

For the time-dependent experiments in artificial Opalinus Clay pore water4 (100/500 µM uranium(VI), pH 5.5) the cells were cultivated in specific media and harvested in the late exponential growing phase. After washing, suspensions containing cells, uranium(VI) and lactate, were incubated at room temperature and samples were taken between zero hours and one week.

RESULTS AND DISCUSSION

The experiments showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h at a concentration of 100 µM. Corresponding UV/Vis measurements of the dissolved cell pellets revealed an increasing proportion of uranium(IV) in the samples with time. After one week round about 40% of the uranium in the cell pellets was reduced. Therefore, the interaction mechanisms can be assigned to a combined sorption-reduction process.
TEM images of the uranium-incubated cells reveal the formation of uranium aggregates on the cell surface. Uranium can be found not only outside the cell in vesicles, but also inside the cell.
HERFD-XANES measurements show the presence of three oxidation states in the cell pellets. Besides uranium(VI) and uranium(IV), also uranium(V) plays a major role in the cellular reduction process. With the help of EXAFS measurements, three cell-related uranium species were detected.
This study helps to close existing gaps in a comprehensive safeguard concept for a final repository for high-level radioactive waste in clay rock. Moreover, new insights into the interaction mechanisms of sulfate-reducing microorganisms with uranium are presented.

REFERENCES

1. A. BAGNOUD et al., “Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock” Nat. Commun., 7, 1-10 (2016).

2. N. MATSCHIVELLI et al., “The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C” Environ. Sci. Technol., 53, 10514-10524 (2019).

3. A. VATSURINA et al., “Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost” Int. J. Syst. Evol. Microbiol., 58, 1228-1232 (2008).

4. P. WERSIN et al., “Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland” Appl. Geochemistry, 26, 931-953 (2011).

Keywords: uranium(VI) reduction; sulfate-reducing microorganisms; Opalinus Clay

  • Poster (Online presentation)
    TransRet2020, 12.-13.10.2021, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33409
Publ.-Id: 33409


Curvature-induced drift and deformation of magnetic skyrmions: Comparison of the ferromagnetic and antiferromagnetic cases

Yershov, K.; Kakay, A.; Kravchuk, V. P.

The influence of the geometrical curvature of chiral magnetic films on the static and dynamic properties of hosted skyrmions are studied theoretically. We predict the effects of the curvature-induced drift of skyrmions under the action of the curvature gradients without any external stimuli. The strength of the curvature-induced driving force essentially depends on the skyrmion type, N\'eel or Bloch, while the trajectory of motion is determined by the type of magnetic ordering: ferro- or antiferromagnetic. During the motion along the surface, skyrmions experience deformations which depend on the its type. In the small-curvature limit, using the collective-variable approach we show, that the driving force acting on a N{\'e}el skyrmion is linear with respect to the gradient of the mean curvature. The driving acting on a Bloch skyrmion is much smaller: it is proportional to the product of the mean curvature and its gradient. In contrast to the fast N{\'e}el skyrmions, the dynamics of the slow Bloch skyrmions is essentially affected by the skyrmion profile deformation. For the sake of simplicity we restrict ourselves to the case of zero Gaussian curvature and consider cylindrical surfaces of general type. Equations of motion for ferromagnetic and antiferromagnetic skyrmions in curved magnetic films are obtained in terms of collective variables. All analytical predictions are confirmed by numerical simulations.

Keywords: skyrmions; curvature effects; ferromagnetic; antiferromagnetic; dynamics

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Publ.-Id: 33408


Evolution of low-lying M1 modes in germanium isotopes

Frauendorf, S.; Schwengner, R.

Magnetic dipole strength functions are determined for the series of germanium isotopes from N = Z = 32 to N = 48 on the basis of a large number of ransition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the 1g 9/2 orbital is analyzed. A bimodal structure comprising an enhancement toward low transition enery and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled 1g 9/2 orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and proves the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature.

Keywords: Nuclear Structure; Nuclear reactions; Magnetic dipole radiation; Photon strength functions; Shell model

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Publ.-Id: 33406


Tungsten (VI) speciation in hydrothermal solutions up to 400°c as revealed by in-situ Raman spectroscopy

Carocci, E.; Truche, L.; Cathelineau, M.; Bazarkina, E.

Tungsten (VI) speciation in hydrothermal solutions is investigated through in-situ Raman spectroscopy coupled to the fused silica glass capillary technique at temperatures up to 400 °C. The effect of temperature, pH, chlorinity and carbonate speciation are evaluated in systems with highly soluble salts Na2WO4 and Na6W12O39. At all investigated temperatures, the tungstate ion WO42- (927 cm-1) is the only W species in solution at pH > 10. At a given pH, the presence of dissolved carbonates and chloride does not affect the tungsten speciation. Tungsten polymers reveal to be stable up to 400 °C under acidic to circum-neutral pH conditions and total tungsten concentration above 0.01 molkgH2O-1-. Among the three observed polymers, namely [W7O24]6- (paratungstate-A, ~ 960 cm-1), [W10O32]4- (tungstate-Y, ~ 970 cm-1), and α-[H2W12O40]6- (α-metatungstate, ~ 990 cm-1), only the hepta and dodeca-tungstate are stable at elevated temperature. Combined with revised literature data, these results allow the thermodynamic stability constants of these W polymers to be constrained, enabling quantitative predictions of their relative abundance at T up to 300 °C. These predictions suggest that W polymerization occurs under hydrothermal conditions even at low W concentration (down to 10-5 mol·kgH2O-1) under acidic conditions. These observations imply that the currently available geochemical models on W transport and deposition in deep and hot geological fluids need to be revised.

Keywords: Tungsten polymers; Polytungstates; Fused silica glass capillary technique; Ore deposits

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Publ.-Id: 33405


Towards nuclear waste confinement: solid solutions and phase stability in (Th/Ce)-Y-zirconia systems

Svitlyk, V.; Weiß, S.; Hennig, C.

INTRODUCTION

Safe disposal of spent nuclear fuel (SNF) requires matrix materials with strong resistance against corrosion and dissolution over a period of 106 years. Derivatives of zirconium-based ceramics, in particular zirconia, ZrO2, are promising materials for these applications since these phases are known to remain stable in geological cycles of up to 109 years. Here scientific and technological goals are to obtain zirconium-based ceramic materials containing maximum possible tetravalent actinides (An) without Zr/An phase separation. In addition, structural stability of these phases under various external parameters, e.g. temperature (T), pressure (P), irradiation and leaching resistance is essential in order to exclude possible discharge of the incorporated radioactive elements over a long time scale.
Five different structural modifications of zirconia are known to exist. At ambient pressure undoped ZrO2 phase exhibits three different polymorphs as a function of temperature - low-temperature (LT) monoclinic (7-fold coordination of Zr atoms, P21/c ) and parent HT tetragonal (T > 1440 K), and cubic (T > 2640 K) forms (8-fold coordination, P42/nmc and Fm-3m, respectively) [1]. Upon application of high pressure (HP) monoclinic modification of zirconia transforms into orthorhombic-I phase (Pbca, 7-fold coordination of Zr atoms similar to that observed for the parent monoclinic P21/c phase) at pressure of ~ 4 GPa [2]. Upon further compression at P > 25 GPa orthorhombic-I modification transforms into orthorhombic-II phase (Pnma, 9-fold coordination) [3] and this phase was found to be stable up to at least 100 GPa [4].
Various properties of ZrO2 can be efficiently controlled by doping. In particular, introduction of Y3+ ions is known to significantly influence phase stability range of zirconia and to stabilize desired HT modifications. Specifically, tetragonal Y-stabilized zirconia (YSZ) phases, denoted as t′, can be obtained at ambient temperature for Y content of ~ 3 - 15 at.% and the cubic YSZ phase can be stabilized for Y content > ~15 at.% [5]. The YSZ phases are, however, much more poorly studied as a function of temperature and pressure compared to the parent ZrO2 compound and the reported results are sometimes contradictory. In this work we present synchrotron radiation diffraction studies on incorporation of Th and Ce atoms in various YSZ phases as a function of composition, temperature and pressure.

DESCRIPTION OF THE WORK

Five series of samples have been synthesized for the current study: ZrxY0.11ThyO2-z (y = 1 – 7%, ~ 1% step), ZrxY0.14ThyO2-z (y = 4, 7, 10, 12%), ZrxY0.21ThyO2-z (y = 0 – 11%, ~ 3% step), ZrxY0.10CeyO2-z (y = 0 – 8%, ~ 1.5% step) and ZrxY0.16CeyO2-z (y = 0 – 8%, ~ 1.5% step). All samples have been obtained via precipitation of the corresponding metal salts by increasing the pH (pH equal 8 for Th- and 11 for Ce-containing samples, correspondingly). Obtained suspensions were subsequently centrifuged and the residues were dried at 350 K. Final oxide phases were formed by annealing at 1673 K for two hours with further quenching.
Ambient, T- and P-dependent in situ synchrotron radiation diffraction experiments were performed at the ROBL BM20 beamline [6] at ESRF, Grenoble. HT was obtained with hot gas blower and HP was generated using diamond anvil cells (DAC). Diffraction data were collected on high resolution XRD1 (Pilatus 100k) and multipurpose XRD2 (Pilatus3 X 2M, HT and HP experiments) diffractometers of ROBL [6].

RESULTS AND DISCUSSION

For the tetragonal ZrxY0.11ThyO2-z and ZrxY0.14ThyO2-z series maximum Th intake was found to be ~ 10 at.%, as concluded from the corresponding expansion of the unit cell volume as a function of % Th (Fig. 1, left). In addition, appearance of ThO2 in the sample with 12 at. % Th also confirms this solubility limit. Introduction of Th atoms into the YSZ system induces flattening of the ZrO8 polyhedra (Fig. 2). This behaviour is explained by the larger ionic radius of Th4+ compared to Ce4+ (1.19 vs. 0.98 Å, respectively, in 8-fold coordination [7]). Thus, insertion of Th atoms introduces additional volume in the unit cell allowing for the coordinating oxygen atoms to arrange in a more symmetrical way with more equilibrated Zr-O distances. Accordingly, the higher Th at. % content may be expected to be favoured by higher (cubic) symmetry. Indeed, cubic ZrxY0.21ThyO2-z system featured intake of Th up to at least 11 at.%, as concluded from the corresponding expansion of the unit cell volume (Fig. 1, right). Investigations in the cubic YSZ system for higher Th content are in progress.
Structural stability of An-containing compounds is one of key requirements for introduction of these materials in the underground nuclear waste repositories (NWR) for long-term storage. This includes resistance against corrosion and internal irradiation. While the underground T-P conditions at the NWR level (typically 500 m below the ground) are rather mild (T ~ 310 K, P ~ 100 bars (or 0.01 GPa)), partial subduction of NWR over a period of million years can not be excluded. This would expose An-containing phases to more extreme temperatures and pressures. In addition, elevated T can be produced in case of a fire outbreak. Therefore, studies of structural stabilities of the corresponding matrix materials under extreme T-P conditions allow to simulate and accelerate processes which can possibly occur during the storage period.
For the corresponding studies we have synthesized Ce-containing YSZ series. Ce is widely used as surrogate atom to simulate tetravalent radioactive elements like Th, U or Pu. In situ T-dependent diffraction studies on tetragonal ZrxY0.10CeyO2-z and cubic ZrxY0.16CeyO2-z series in a RT-1150 K range revealed excellent structural stability for all the studied compounds. In particular, occupancy of Ce4+ atoms as a function of temperature does not decrease in these systems (Fig. 3, Ce0.05Y0.10Zr0.85O1.95 phase is shown as an example) indicating that the mobility of these ions does not increase with temperature. Within the error range unit cell volume increases linearly for all the phases. The corresponding coefficients of thermal expansion, defined as α = 1/V0*((V-V0)/(T-T0)), with V0(V) and T0(T) being the initial (final) unit cell volume and the sample temperature, are listed in Table 1. Cubic Ce-YSZ samples are slightly stiffer than the corresponding tetragonal phases.
Application of external pressure on the Ce0.05Y0.10Zr0.85O1.95 phase induced a structural transformation to a higher cubic symmetry around the P ~ 8.5 GPa. Interesting, occupancy of Ce4+ remains stable throughout the transition. This together with T-dependent data indicates excellent affinity of Ce atoms with the host YSZ matrices. The parent YSZ phases are, therefore, promising candidates as host matrices for radiotoxic tetravalent elements like U, Th or Pu.

ACKNOWLEDGEMENTS

We acknowledge the Federal Ministry of Education and Research (Germany) for the support of this project (BMBF grant 02NUK060).

REFERENCES

1. M. Bocanegra-Bernal et al., “Phase transitions in zirconium dioxide and related materials for high performance engineering ceramics,” J. Mater. Sci., 37, 4947, 2002. 2. O. Ohtaka et al., “Structural Analysis of Orthorhombic ZrO2 by High Resolution Neutron Powder Diffraction,” Proc. Jpn. Acad. Ser. B, 66, 193, 1990. 3. J. Haines et al., “Crystal Structure and Equation of State of Cotunnite-Type Zirconia,” J. Am. Ceram. Soc., 78, 2, 445, 1995. 4. O. Ohtaka et al., “Phase relations and equation of state of ZrO2 to 100GPa,” J. Appl. Crystallogr., 38, 5, 727–733, 2005. 5. H. G. Scott, “Phase relationships in the zirconia-yttria system,” J. Mater. Sci., 10, 9, 1527, 1975. 6. A. C. Scheinost et al., “ROBL-II at ESRF: a synchrotron toolbox for actinide research,” J. Synchr. Rad., 28, 1, 333, 2021. 7. R. D. Shannon, “Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides,” Acta Crystallogr. Sect. A, 32, 5, 751, 1976.

Related publications

  • Contribution to proceedings
    TransRet2020 - Workshop on Processes Influencing Radionuclide Transport and Retention, 12.-13.10.2021, Karlsruhe, Online, Germany

Permalink: https://www.hzdr.de/publications/Publ-33404
Publ.-Id: 33404


Smart Kd-concept as efficient approach to improve geochemistry in reactive transport modelling

Stockmann, M.; Lu, R.; Gehrke, A.; Montoya, V.; Noseck, U.; Brendler, V.

A key component of risk assessment for radioactive waste repositories in deep geological formations is the prediction of potential radionuclide (RN) transport through the geosphere. One big challenge for such large-scale heterogeneous transport simulations is the integration of realistic geochemical models and their parameters at affordable computational costs. Sorption on minerals is an important retardation process and typically applying constant distribution coefficients (Kd) that can be easily included in reactive transport codes. One of the advantage of this approach is the computational efficiency, but it cannot reflect changes in geochemical conditions. On the other hand, mechanistic surface complexation models used for process understanding can be directly coupled to transport codes with geochemical solvers, but usually only at high computational costs. An alternative is provided by the smart Kd concept (www.smartkd-concept.de) [1], specifically developed to describe variable RN sorption in transport models as consequence of changing geochemical conditions over space and time. The philosophy behind this concept is to compute multidimensional look-up tables storing distribution coefficients - but here referred to as smart Kd as they are based on mechanistic sorption models. These tables can cover wide ranges of important geochemical parameters, e.g. pH, ionic strength, and concentrations of dissolved ions. The information stored in such a look-up table can be accessed by reactive transport codes at each simulation step. This approach was already implemented in the code d3f++ [2]. Here, an additional implementation and validation of the smart Kd-approach in the code OpenGeoSys OGS6 [3, 4] is presented. The application case selected is sorption of repository-relevant RNs and possible migration scenarios through a typical sedimentary rock system covering potential host rock formations in Northern Germany. This serves as a comprehensive proof-of-concept and demonstrates the capability to describe the sorption behaviour in dependence of changing geochemical conditions quite well. As a side-effect, the large Kd-matrices that were computed can be further analysed by sensitivity and uncertainty analysis (SA/UA). Results of this case study showed that the smart Kd-approach goes considerably beyond the conventional concepts. We can illustrate that constant Kd values previously used in transport simulations are rough approximations (and not necessarily conservative ones), as in reality they rather range over several orders of magnitude. Moreover, with the results from the SA, those input parameters influencing strongest the radionuclide retardation can be identified. The results of the transport simulations with the newly implemented smart Kd-approach showed a good agreement to full reactive transport simulations using PHAST [5] or a direct coupling OGS6#PhreeqC and reflect a radionuclide-specific retardation effect. This real application case serves as a benchmark for field-scale transport simulations.

  • Lecture (Conference) (Online presentation)
    Tagung der Fachsektion Hydrogeologie der Deutschen Geologischen Gesellschaft (FH-DGGV-Tagung), 23.-26.03.2022, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33403
Publ.-Id: 33403


Ein „Wireless Sensor Network“ zur Prozesscharakterisierung in Biogasfermentern

Buntkiel, L.; Budelmann, C.; Heller, A.; Annas, S.; Reinecke, S.; Hampel, U.

Kenntnisse über die Durchmischung und die Strömungsvorgänge in Biogasfermentern ermöglichen Optimierungspotenziale bezogen auf die Vermischung, aber auch auf die Biogasausbeute und Energieeinsparung. Aufgrund der Beschaffenheit der Fermenter (große Abmessungen, Stahlbeton) und des Biosubstrats (nicht opakes Fluid) gibt es derzeit kein Messsystem, um Strömungen und räumlich verteilte Prozessparameter zu vermessen. In dem Projekt „NeoBio“ wurde dazu eine Wireless Sensor Network (WSN) entwickelt.

Keywords: Wireless Sensor Network; Sensorpartikel; Biogas; Abwasser

  • Open Access Logo Contribution to proceedings
    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland
    Biogas in der Landwirtschft - Stand und Perspektiven, Darmstadt: KTBL, 978-3-945088-83-8
  • Open Access Logo Poster (Online presentation)
    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland
  • Open Access Logo Lecture (Conference) (Online presentation)
    Biogas in der Landwirtschaft, 29.-30.09.2021, Online, Deutschland

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Permalink: https://www.hzdr.de/publications/Publ-33402
Publ.-Id: 33402


Radiolabeled Silicon-Rhodamines as Bimodal PET/SPECT-NIR Imaging Agents

Kanagasundaram, T.; Laube, M.; Wodtke, J.; Kramer, S. C.; Stadlbauer, S.; Pietzsch, J.; Kopka, K.

Radiolabeled fluorescent dyes are decisive for bimodal imaging as well as highly in demand for nuclear- and optical imaging. Silicon-rhodamines (SiRs) show unique near-infrared (NIR) optical properties, large quantum yields and extinction coefficients as well as high photostability. Here, we describe the synthesis, characterization and radiolabeling of novel NIR absorbing and emitting fluorophores from the silicon-rhodamine family for use in optical imaging (OI) combined with positron emission tomography (PET) or single photon emission computed tomography (SPECT), respectively. The presented photostable SiRs were characterized using NMR-, UV-Vis-NIR-spectroscopy and mass spectrometry. Moreover, the radiolabeling conditions using fluorine-18 or iodine-123 were extensively explored. After optimization, the radiofluorinated NIR imaging agents were obtained with radiochemical conversions (RCC) up to 70% and isolated radiochemical yields (RCY) up to 54% at molar activities of g.t. 70 GBq/µmol. Radioiodination delivered RCCs over 92% and allowed to isolate the 123I-labeled product in RCY of 54% at a molar activity of g.t. 7.6 TBq/µmol. The radiofluorinated SiRs exhibit in vitro stabilities g.t. 70% after two hours in human serum. The first described radiolabeled SiRs are a promising step toward their further development as multimodal PET/SPECT-NIR imaging agents for planning and subsequent imaging-guided oncological surgery.

Keywords: multimodal imaging; PET imaging; SPECT imaging; optical imaging; organic chemistry; near-infrared fluorophores; silicon-rhodamines; radiochemistry; radiofluorination; radioiodination

Permalink: https://www.hzdr.de/publications/Publ-33401
Publ.-Id: 33401


4D log file-based proton dose reconstruction: Fraction-wise interplay analysis in clinical practice

Spautz, S.; Thiele, J.; Tschiche, M.; Troost, E. G. C.; Richter, C.; Stützer, K.

Purpose/Objective
Pencil beam scanning (PBS) proton therapy (PT) in patients with intra-fraction, breathing-induced tumour motion might result in unrecognized deviations from the planned dose distribution. Our work pursued the clinical roll-out of a 4D log file-based proton dose reconstruction (4DlogReco). By that, we monitor the interplay effect and study its relevancy in an ongoing clinical study at the University Proton Therapy Dresden (UPTD).

Material/Methods
We had developed and experimentally validated a 4DlogReco (in RayStation v.8) based on amplitude-sorted 4DCTs, PBS machine log files and synchronized motion log files. The workflow and data handling was verified in the clinical treatment planning system by a retrospective analysis of four complete PBS-PT treatment series (incl. lung, oesophageal and pancreatic carcinoma; mean motion ≤5mm; 20-33 fractions) of patients who received weekly in-room 4DCTs for monitoring interfraction changes. For the final 4DlogReco translation into clinical practice, we initiated the MOBIL study (Monitoring Of Breathing for Interplay study with Logfiles).
Available patient data were analysed fraction-wise (Fig1). We considered individual critical organs at risk (OAR; lung, heart, spinal cord, kidneys, oesophagus), the clinical target volume (CTV) coverage, mean dose, near-maximum dose and homogeneity index [D98, Dmean, D1, HI=(D1-D98)/Dprescribed] and the deviations from the plan in the fraction-wise worst case (Δwc) and in the accumulated dose (Δacc).

Results
The 4DlogReco was successfully translated into clinical application. So far, two patients (oesophageal and pancreatic carcinoma; mean motion ≤5mm; 19 and 30 fractions) had been treated within the MOBIL study. Daily 4DlogReco took about 15min incl. data processing and dose calculation, and should speed up by an automatic log file retrieval and GPU-based dose calculation after TPS upgrade.
For the six investigated patients (incl. the four workflow test patients), intra-fraction motion led to CTV parameter differences in the worst-case fractions of Δwc(D98)=( 15.5 – 3.4)pp, Δwc(D1)=( 0.1 – 3.5)pp and Δwc(HI)=0.04 – 0.17, while there were smaller changes in the accumulated dose of Δacc(D98)=( 2.6 – -0.6)pp, Δacc(D1)=(-1.3 – 0.4)pp and Δacc(HI)=0.00 – 0.03 (Fig2). The individually relevant OAR dose parameters remained uncritical in line with the so far investigated minor motion amplitudes.

Conclusion
The first 4DlogReco workflow capable to deal correctly with amplitude-sorted 4DCTs provides a fraction-wise verification of the interplay-affected delivered and accumulated dose to moving targets. The clinical implementation of this QA module at UPTD had a direct influence on our institutional treatment protocols, as PBS-PT of lung cancer patients is now admissible for motions up to 15mm. The monitoring of such patients will provide valuable insights on the necessity of further motion compensation and of considering the accumulated 4DlogReco doses during treatment adaptation.

Keywords: PBS proton therapy; Interplay assessment; Log file-based dose reconstruction

  • Open Access Logo Lecture (Conference)
    ESTRO 2022, 06.-10.05.2022, Kopenhagen, Denmark

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Permalink: https://www.hzdr.de/publications/Publ-33400
Publ.-Id: 33400


Dynamically assisted tunneling in the impulse regime

Kohlfürst, C.; Queißer, F.; Schützhold, R.

We study the enhancement of tunneling through a potential barrier V(x) by a time-dependent electric field with special emphasis on pulse-shaped vector potentials such as A(t)=A0/cosh^2(ωt). In addition to the known effects of pre-acceleration and potential deformation already present in the adiabatic regime, as well as energy mixing in analogy to the Franz-Keldysh effect in the non-adiabatic (impulse) regime, the pulse A(t) can enhance tunneling by ``pushing'' part of the wave-function out of the rear end of the barrier. Besides the natural applications in condensed matter and atomic physics, these findings could be relevant for nuclear fusion, where pulses A(t) with ω=1 keV and peak field strengths of 10^16 V/m might enhance tunneling rates significantly.

Keywords: Tunneling & traversal time; Nuclear fusion; Schroedinger equation

Permalink: https://www.hzdr.de/publications/Publ-33399
Publ.-Id: 33399


On the correlation of angular distributions of keV ions and trajectory-dependent electronic excitations in transmission channelling geometry

Holeňák, R.; Lohmann, S.; Komander, K.; Primetzhofer, D.

We use energy discrimination of keV ions transmitted through a thin, single-crystalline silicon membrane to correlate specific angular distribution patterns formed in channelling geometry with trajectory-dependent electronic energy loss. The integral energy and intensity distribution of transmitted ions can thus be dissected into on one side axially channelled projectiles travelling along rather straight trajectories and on the other side dechannelled projectiles predominantly experiencing blocking. Angular distributions of transmitted ions are further simulated with two different Monte-Carlo codes.

Keywords: Channelling; keV ions; Monte-Carlo; Time-of-flight

  • Open Access Logo Contribution to proceedings
    25th International Conference on Ion Beam Analysis & 17th International Conference on Particle Induce X-ray Emission & International Conference on Secondary Ion Mass Spectrometry, 11.10.2021, Online, Online
    Journal of Physics: Conference Series, Volume 2326, 012008
    DOI: 10.1088/1742-6596/2326/1/012008
    arXiv: arXiv:2111.06809

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Permalink: https://www.hzdr.de/publications/Publ-33398
Publ.-Id: 33398


Towards Optimized Bioavailability of 99mTc‑Labeled Barbiturates for Non‑invasive Imaging of Matrix Metalloproteinase Activity

Honold, L.; Austrup, M.; Faust, A.; Konken, C.; Schwegmann, K.; Zinnhardt, B.; Daniliuc, C.; Haufe, G.; Schäfers, M.; Kopka, K.; Hermann, S.

Introduction: Dysregulated activity of matrix metalloproteinases (MMPs) drives a variety of pathophysiological conditions. Non-invasive imaging of MMP activity in vivo promises diagnostic and prognostic value. However, current targeting strategies by small molecules are typically limited with respect to the bioavailability of the labeled MMP binders in vivo. To this end, we here introduce and compare three chemical modifications of a recently developed barbiturate-based radiotracer with respect to bioavailability and potential to image MMP activity in vivo.
Methods: Barbiturate-based MMP inhibitors with an identical targeting unit but varying hydrophilicity were synthesized, labeled with technetium-99m, and evaluated in vitro and in vivo. Biodistribution and radiotracer elimination were determined in C57/BL6 mice by serial SPECT imaging. MMP activity was imaged in a MMP-positive subcutaneous xenograft model of human K1 papillary thyroid tumors. In vivo data were validated by scintillation counting, autoradiography, and MMP immunohistochemistry.
Results: We prepared three new 99mTc-labeled MMP inhibitors, bearing either a glycine ([99mTc]MEA39), lysine ([99mTc]MEA61), or the ligand HYNIC with the ionic co-ligand TPPTS ([99mTc]MEA223) yielding gradually increasing hydrophilicity. [99mTc]MEA39 and [99mTc]MEA61 were rapidly eliminated via hepatobiliary pathways. In contrast, [99mTc]MEA223 showed delayed in vivo clearance and primary renal elimination. In a thyroid tumor xenograft model, only [99mTc]MEA223 exhibited a high tumor-to-blood ratio that could easily be delineated in SPECT images.
Conclusion: Introduction of HYNIC/TPPTS into the barbiturate lead structure ([99mTc]MEA223) results in delayed renal elimination and allows non-invasive MMP imaging with high signal-to-noise ratios in a papillary thyroid tumor xenograft model.

Keywords: Barbiturates; Matrix metalloproteinase inhibitors; Pyrimidine-2,4,6-triones Single photon emission; Single photon emission computed tomography; Tumor imaging

Permalink: https://www.hzdr.de/publications/Publ-33397
Publ.-Id: 33397


Impact of Ion-Ion Correlations on the Adsorption of M(III) (M = Am, Eu, Y) onto Muscovite (001) in the Presence of Sulfate

Neumann, J.; Lee, S. S.; Brinkmann, H.; Eng, P.; Stubbs, J.; Stumpf, T.; Schmidt, M.

The environmental fate of metal ions is influenced by their interactions with natural organic and inorganic ligands, which modify the ions’ structure and charge and thus influence their interactions with mineral phases. We investigate the impact of ubiquitous sulfate on the retention of trivalent f-element cations (M(III) = Am, Eu, Y) by muscovite. We combine ex situ alpha spectrometry and in situ surface X-ray diffraction (i.e., crystal truncation rod and resonant anomalous X-ray reflectivity) to determine M(III) coverages and interfacial structures at the molecular level. M(III) cations adsorb as two distinct outer-sphere (OS) complexes (i.e., adsorbed and extended OS complexes) whose coverages vary with increasing sulfate concentration, [SO42-]. When [SO42-] ≤ 0.4 mM, coverages increase and exceed the amounts needed for surface charge compensation of muscovite by a factor of ~3. This overcompensation is likely controlled by ion-ion correlations at the mineral/water interface rather than adsorption of MSO4+, which has a lower thermodynamic stability in the solutions and weaker electrostatic attraction to the mica surface than M3+. For higher [SO42-], MSO4+ and M(SO4)2- dominate solution speciation, leading to a strong decrease of the M(III) coverage due to their lower sorption affinity and weaker ion-ion correlations compared to M3+.

Keywords: Surface X-ray diffraction; Solid liquid interface; electrolyte effect; overcompensation; rare earth elements; actinides

Permalink: https://www.hzdr.de/publications/Publ-33395
Publ.-Id: 33395


Impact of background electrolyte composition on the interfacial formation of Th(IV) NPs on mica (001)

Neumann, J.; Qiu, C.; Eng, P.; Stumpf, T.; Schmidt, M.

A mechanistic understanding of the formation of actinide nanoparticles (NPs) and its impact on the mobility of radionuclides in the environment is important for a reliable risk assessment of repositories for radioactive waste. Previous studies using surface x-ray diffraction (SXD) reported an unexpected impact of electrolyte composition on the sorption of Th(IV) on the muscovite (001) basal plane. Th uptake decreased following an unexpected trend: LiClO4 > KClO4 > NaClO4. A significantly higher coverage than needed for surface charge compensation (0.25 Th/AUC, AUC = 46.72 Ų, area of mica (001) unit cell) was observed for LiClO4 (4.9 Th/AUC), suggesting the formation of Th-NPs [1]. It remained unclear, if the electrolyte affects a reaction at the mineral surface or in solution.
We combined SXD and in situ AFM to address this question. At low [Th] (0.1 mM), the investigated electrolytes include LiCl and KCl, in comparison with the reported Th uptakes for the respective perchlorate electrolytes, and the series is extended to NH4Cl and CsCl. The results are compared to reported value for NaCl [2]. The interfacial structures show an extremely broad distribution of Th electron density up to 50 Å from the surface for LiCl and KCl. A decrease of Th uptake within the alkali series is found (Figure 1). A strong linear correlation (R2 = 0.9962) between Th uptake and ionic radius of the alkali metal ion is found, indicating that sorption competition between Th4+ and the electrolyte cation is the origin of the observed effect. The value for NaCl is a clear outlier in this series, showing a much lower uptake of Th than expected according to the trend.
Perfect agreement between the number of formed particles per area, obtained by in situ AFM, and Th uptake, observed by SXD, is found. Particles show a vertical size of ~1 – 2 nm and lateral dimensions of ~10 – 20 nm, indicating that retention occurs by the formation of NPs at the mineral-solution interface (heterogeneous nucleation), which is strongly influenced by the electrolyte.
Additionally, SXD was performed at higher [Th] = 3 mM, where the formation of Th oligomers in solution is expected. Under these conditions, LiCl (2.0 Th/AUC), NaCl (1.4 Th/AUC), and KCl (1.7 Th/AUC) show similar Th uptake, indicating a much smaller impact of electrolyte composition. The obtained interfacial structures are dominated by a high Th loading at a distinct distance (~ 6.5 Å) from the muscovite surface. Therefore, the main retention mechanism at high [Th] is suggested to be the (electrolyte-independent) formation of Th oligomers in solution and their subsequent sorption on the mineral surface.

References
[1] - M. Schmidt et al., Geochim. Cosmochim. Acta. 165, 280–293 (2015).
[2] - M. Schmidt et al., Geochim. Cosmochim. Acta. 88, 66–76 (2012).

Related publications

  • Poster (Online presentation)
    ESRF User Meeting 1-2021, 08.-10.02.2021, Grenoble, Frankreich
  • Poster (Online presentation)
    APS/CNM User Meeting 2021, 10.-14.05.2021, Lemont, USA

Permalink: https://www.hzdr.de/publications/Publ-33394
Publ.-Id: 33394


Structural Investigation of the Adsorption von Y(III) on Orthoclase (001) Single Crystals using Resonant Surface X ray Diffraction

Neumann, J.; Lessing, J.; Demnitz, M.; Eng, P.; Stubbs, J.; Stumpf, T.; Schmidt, M.

INTRODUCTION

Transport of radionuclides (RNs), from deep geological repositories for radioactive waste, such as the highly toxic trivalent minor actinides (An(III)) Am and Cm, will be controlled by their interactions with charged mineral phases. Many countries such as Finland, Sweden, and Germany consider a repository in crystalline rock, which contains large amounts of feldspars, e.g. orthoclase (K-feldspar). Hence, reliable risk assessments of potential repository sites depend on a fundamental understanding of sorption quantity and structure of An(III) on feldspars. Typically, those interactions are investigated using mineral powder samples [1], which depict an idealization of the natural system due to the small grain size of the mineral. In those studies, information about macroscopic effects on sorption processes, like crystal orientation or surface roughness, are not accessible. Therefore, in this work we study the adsorption of Y(III), as an inactive rare earth analogue for An(III), on natural single crystal orthoclase samples of the (001) crystal orientation using the modern synchrotron-based, surface X-ray diffraction technique.

DESCRIPTION OF THE WORK

Natural single crystal orthoclase samples were freshly cleaved along their (001) orientation and reacted overnight in a solution of [Y3+] = 0.01 M at pH = 5.0 or 6.9. After the reaction was finished, surface X-ray diffraction (SXRD) was measured in situ at beamline 13 ID-C (GeoSoilEnviroCARS) of the Advanced Photon Source at Argonne National Laboratory. SXRD yields the total electron density profile of the mineral/water interface by measuring crystal truncation rods (CTR). For the first time, resonant anomalous X-ray reflectivity (RAXR) is applied on orthoclase for identification and quantification of sorption species, in our case Y3+. Coverage of adsorbed Y3+ is given in units of Y/AUC (area of the orthoclase (001) unit cell = 55.57 Å2).

RESULTS AND DISCUSSION

The study investigates the adsorption of Y3+ on orthoclase (001) at two different pH values. RAXR spectra of both samples show strong modulations at the Y X-ray absorption edge (17.038 keV), indicating that Y3+ has been adsorbed to the orthoclase surface. Analysis of amplitudes and phases of the RAXR spectra yield information about coverage and distance of the adsorbed species from the surface.
At pH 5.0, two sorption species at a distance of 2.47 (Species A) and 8.35 Å (Species B1) from the uppermost oxygen-atoms (Osurf) of the mineral surface are identified. At higher pH (6.9), the adsorbed Y is located at a distance of 1.50 (Species C) and 4.38 Å (B2) from Osurf. The Y3+ aquo ion has hydration shells in a distance of 2.36 and 4.40 Å. Therefore, Species A can be attributed to an outer-sphere (OS) and species B1 and B2 to extended outer-sphere (EOS) sorption complexes. In contrast, Species C is closer to the surface than any other sorption species observed in this study. At the investigated pH of 6.9, more sites of the orthoclase surface are deprotonated, obviously leading to the release of parts of the hydration shell of Y. Therefore, Species C is interpreted as an inner-sphere (IS) sorption complex. A plausible, bidentate binding motif for Species C is suggested based on the obtained results, where Y3+ is bound to two nearest Osurf resulting in a Y-O bond length of 2.46 Å in an angle of 39.0°.
While the interfacial speciation between the two samples is different, the total Y coverage is found to be similar for both samples (~0.6 Y/AUC). At pH 6.9 more than 70 % of the adsorbed Y3+ is bound as IS complex (Species C, 0.43 Y/AUC). The obtained coverage of the IS complex corresponds to ~2/3 of an adsorbed Y3+ monolayer, assuming bidentate coordination to two Osurf. Overall, the obtained sorption quantity and interfacial speciation are in good agreement with the powder studies, supporting the applicability of the previously developed SCMs to simulate retention of An(III) by K-feldspar for macroscopic systems.
However, we also identify reasonable amounts of adsorbed EOS complexes that are typically not found in studies using mineral powders and therefore not considered thermodynamic models. This result points out the need of studies working on macroscopic mineral samples to assess the impact of those species, and more general the controlling parameters relevant for natural systems, such as crystal orientation, surface roughness, and a realistic solid-liquid ratio. In conclusion, the results of this study contribute to a more realistic and reliable prediction of the mobility of trivalent actinides in the environment, and will enable a better risk assessment for deep geological repositories for radioactive waste.

  • Lecture (Conference)
    TransRet Workshop: Processes Influencing Radionuclide Transport and Retention, 12.-13.10.2021, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33393
Publ.-Id: 33393


f-element sorption onto K-feldspar – A comprehensive characterization of mechanism and thermodynamics

Neumann, J.; Brinkmann, H.; Britz, S.; Lützenkirchen, J.; Bok, F.; Stockmann, M.; Brendler, V.; Stumpf, T.; Schmidt, M.

The mobility of radionuclides in the environment, in particular in the context of a deep geological repository for radioactive waste, is heavily influenced by their interactions with charged mineral surfaces. This study investigates the retention potential of feldspars, a main component of granite as one potential host rock for a repository. The focus is on the sorption of trivalent actinides (Am, Cm) and their rare earth analogues (Eu, La, Lu, Nd, Y) as a main source of radiotoxicity in spent nuclear fuel.
A multi-method approach was used, consisting of traditional batch sorption experiments over a broad range of experimental conditions to determine uptake. Generally, retention increases with increasing pH and reaches quantitative retention at near neutral conditions. Furthermore, a spectroscopic study of the sorption structure on the molecular level was conducted. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) using the actinide Cm as a luminescent probe, shows that four surface complexes are formed, an inner sphere sorption complex and its two hydrolysis forms, as well as a ternary feldspar/Cm/silicate complex at alkaline conditions (pH > 10).
Based on the observed comprehensive batch sorption dataset a generic surface complexation model (SCM-A) was developed that describes sorption of trivalent actinides and their rare earth analogues as a function of a variety of geochemical parameters (pH, ionic strength, metal concentration, solid-liquid ratio,…). In a second step, the dataset for the model was further increased by taking the quantitative spectroscopic results into consideration (SCM-B).
The developed SCMs deliver surface complexation parameters of the formed sorption species, which are included in thermodynamic databases. This data is essential for the subsequent calculation of distribution coefficients in modern approaches like the Smart KD-concept[1] as well as reactive transport modeling. Therefore, this study provides a contribution to a more reliable safety assessment of repositories for radioactive waste.[2]
[1] Stockmann, M. et al., "Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems", Chemosphere., 187, 277–285 (2017).
[2] Neumann, J. et al., "A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar", J. Colloid Interface Sci. (2020). https://doi.org/10.1016/j.jcis.2020.11.041.

  • Lecture (Conference) (Online presentation)
    Goldschmidt Konferenz, 04.-09.07.2021, Lyon, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-33392
Publ.-Id: 33392


Umfassende Untersuchung und Bestimmung thermodynamischer Daten der Sorption von dreiwertigen Metallionen an K-Feldspat

Neumann, J.; Brinkmann, H.; Britz, S.; Lützenkirchen, J.; Bok, F.; Stockmann, M.; Brendler, V.; Stumpf, T.; Schmidt, M.

1 Introduction
Transport of contaminants, e.g. radionuclides, in the environment depends strongly on their interactions with mineral phases. In a repository for radioactive waste, crystalline rock (e.g. granite) as one potential host rock in Germany and many other countries, may affect the mobility of radionuclides. Main constituents of granite are feldspars. In spent nuclear fuel, trivalent actinides (Am, Cm, but also Pu) contribute strongly to the radiotoxicity. Therefore, this work studies the retention of Am and Cm, as well as their rare earths element analogues (Eu, La, Lu, Nd, Y) on K-feldspar. By combining batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS), a generic surface complexation model (SCM) was obtained that is valid for all investigated M3+. Thermodynamic sorption data were obtained and an understanding of sorption mechanisms on the molecular level was achieved.
2 Results
Batch sorption experiments were performed over a broad range of environmental conditions (pH 4 – 10, [M3+] = 52 nM – 10 µM, 3 – 50 g/L K-feldspar (dp < 21 µm; 63 – 200 µm))[1]. Sorption is weak for pH < 5, strongly increases between pH 5 – 7 and reaches complete uptake at higher pH. By deconvolution of Cm emission spectra, an inner-sphere complex and its first two hydrolysis forms were found to be responsible for retention in this pH range.
For determination of the deprotonation constant pKa of K-feldspar, as one important input parameter of the model, column titration experiments were conducted. Batch sorption results of all studied M3+ were used to develop two alternative SCMs. The experimental sorption data were used to determine surface complexation parameters by coupling the parameter estimation code UCODE with PHREEQC (SCM-A). In a second approach, spectroscopic data were also considered (SCM-B). A generic approach was used to develop the geochemical models that satisfactorily describe all of the derived M3+/K feldspar sorption edges as well as TRLFS-derived speciation. The model delivered respective stability constants of the sorption complexes, which were added to the data base of the Smart Kd-concept[2]. Therefore, this work improves the risk assessment of repositories for radioactive waste.

Figure 1: Experimental batch sorption data (symbols) and calculation results using the two developed SCMs for different experimental conditions.[1]
References
[1] Neumann, J. et al., "A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar", J. Colloid Interface Sci. (2020). https://doi.org/10.1016/j.jcis.2020.11.041.
[2] Stockmann, M. et al., "Smart Kd-values, their uncertainties and sensitivities - Applying a new approach for realistic distribution coefficients in geochemical modeling of complex systems", Chemosphere., 187, 277–285 (2017).

Keywords: sorption; trivalent; lanthanides; actinides; K-feldspar; TRLFS; SCM

  • Lecture (Conference) (Online presentation)
    Tage der Standortauswahl, 11.-12.02.2021, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33391
Publ.-Id: 33391


Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-based Two-Dimensional Conjugated Covalent Organic Frameworks

Zhong, H.; Wang, M.; Ghorbani Asl, M.; Zhang, J.; Hoang Ly, K.; Liao, Z.-Q.; Chen, G.; Wei, Y.; Biswal, B. P.; Zschech, E.; Weidinger, I. M.; Krasheninnikov, A.; Dong, R.; Feng, X.

Electrochemical N₂ reduction reaction (NRR) under ambient conditions is attractive for the great potential in replacing the current Haber-Bosch process towards sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising electrocatalysts for NRR. However, simultaneously boosting their activity and selectivity toward NRR remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M-N₄-C centers as novel, defined and effective catalysts, and achieve a simultaneous enhancement in the activity and selectivity towards electrochemical NRR to yield ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn and Cu) and pyrene building blocks bonded by pyrazine linkages. Significantly, the 2D c-COF catalysts with Fe-N₄-C center exhibit higher ammonia yield rate (33.6 μg h⁻¹mg⁻¹cat) and Faradaic efficiency (FE, 31.9 %) at -0.1 V vs. reversible hydrogen electrode than those with other M-N₄-C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h⁻¹mg⁻¹cat and FE >30 %). In-situ X-ray absorption spectroscopy, Raman spectroelectrochemistry and theoretical calculations unveil that the Fe-N₄-C center acts as a catalytic site. It shows a unique electronic structure with localized electronic states at the Fermi level, allowing for higher N₂ affinity and stronger binding energy of N₂, enabling faster N₂ activation and NRR kinetics than other M-N₄-C centers. Our work opens the possibility of developing metal-nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalysts and provides an atomic understanding of the NRR process on M-Nx-C based electrocatalysts for the design of high-performance NRR catalysts

Keywords: Covalent Organic Frameworks; Two-dimensional; Electrocatalyst; Nitrogen reduction reaction

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Publ.-Id: 33390


Data Publication: Development of [18F]LU14 for PET Imaging of Cannabinoid Receptor Type 2 in the Brain

Moldovan, R.-P.

Cannabinoid receptors type 2 (CB2R) represent an attractive therapeutic target for neurodegenerative diseases and cancer. Aiming at a positron emission tomography (PET) radiotracer to monitor receptor density and/or occupancy during a CB2R-tailored therapy, we developed here cis-[18F]1-(4-fluorobutyl-N-((1s,4s)-4-methylcyclohexyl)-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carboxamide ([18F]LU14) starting from the corresponding mesylate precursor. First biological evaluation revealed that [18F]LU14 is a highly affine CB2R radioligand with >80% intact tracer in brain at 30 min p.i. Its further evaluation in a well-established rat model of CB2R overexpression by PET demonstrated its ability to selectively image the CB2R in the brain and its potential as tracer to further investigate diseased related CB2R changes in expression.

Keywords: Cannabinoid receptor type 2; naphtyrid-2-one; binding affinity; radiochemistry; fluorine-18 labeling; brain; positron emission tomography

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Publ.-Id: 33389


An AMS-world without any chemistry? – Untypical measurements of ²⁶Al, ⁴¹Ca and ⁵⁵Fe

Merchel, S.; Golser, R.; Lachner, J.; Marchhart, O.; Martschini, M.; Rugel, G.; Wallner, A.; Walther, D.; Wieser, A.

AMS measurements typically are lasting minutes to hours, but are usually preceded by time-consuming (typically days to weeks of) chemical preparation. Both, physicists and chemists are dreaming of an AMS-world without any chemistry.

Some of our earlier studies have already proven AMS being reasonable, fast and easily accessible for ⁷Be [1] and ⁴¹Ca [2] analysis if largely reducing radiochemical separation. However, to our knowledge there are only a few cases completely omitting wet chemical separation, e.g., ¹⁰Be/⁹Be in a Be mineral (phenakite) [3] and ¹⁴C/¹²C by laser-ablation AMS of stalagmites and corals [4]. Here, we focus on two new examples for “Instrumental” AMS (IAMS) at the DREsden AMS (DREAMS) facility and the Vienna Environmental Research Accelerator (VERA):

First, a pilot study to quantify ⁵⁵Fe (t₁/₂=2.76 a) in steel from a reactor vessel of a nuclear power plant by IAMS was validated (after radiochemical separation) by liquid scintillation counting (LSC) and AMS [5]. DREAMS reaches an uncertainty <10% at the 1 kBq g(Fe)⁻¹ level within 10 min measuring unprocessed steel chips. The background (<3 Bq g(Fe)⁻¹) is limited by the short measurement time. IAMS for analysing ⁵⁵Fe from neutron-capture production is reasonable and fast compared to other analytical methods.

Secondly, the ILIAMS set-up at VERA (Martschini et al., this meeting) allows to determine ratios of ²⁶Al (t₁/₂=0.7 Ma) to ²⁷Al and ⁴¹Ca (t₁/₂=0.104 Ma) to ⁴⁰Ca in stony meteorites by IAMS. The nearly complete suppression of isobars, i.e., ²⁶MgO⁻, when extracting AlO⁻, and ⁴¹KF₃⁻ when extracting CaF₃⁻, make pressure digestion (HF/HNO₃), ion exchange and precipitations unnecessary. Most stony meteorites contain ~1% Al, mainly in the form of Na-rich-Ca-poor plagioclase ((Na,Ca)(Si,Al)₄O₈)). Additional sources for >1% Ca are pyroxene (CaMgSi₂O₆) and phosphates (mainly apatite: Ca₅(PO₄)₃Cl)) [6]. IAMS has been performed using 1-2 mg representative powder of the previously-investigated chondrite Dhurmsala [7], either pure, mixed with Fe or PbF₂ powder.

For IAMS of ²⁶Al, AlO⁻ currents from Dhurmsala were - independent of mixing with Fe or pure - about 2% of Al₂O₃(Fe) ones. At ²⁶Al/²⁷Al of ~1.3x10⁻¹⁰ statistical uncertainties of 3% are reached within 15 min sputtering while cathodes last several hours. IAMS data at VERA - in the presence of about 15% Mg - are comparable to earlier (chemical processing) AMS results at DREAMS and ETH Zurich.

For IAMS of ⁴¹Ca, very stable CaF₃⁻ currents from Dhurmsala are ~5% of chemically-processed CaF₂ ones (each mixed with PbF₂). At ~1x10⁻¹¹ ⁴¹Ca/Ca, count rates of 1 min⁻¹ sputtering time are reached. IAMS data measured in the presence of about 1‰ K at VERA are comparable to earlier (chemical processing) AMS results at ANU, DREAMS and ETH Zurich.

The major uncertainty for both nuclides, originating from the current differences of standards and samples, will be addressed soon.

References: [1] Tiessen et al., JRNCh 319 (2017) 965. [2] Hampe et al., JRNCh 296 (2013) 617. [3] Merchel et al., JRNCh 298 (2013) 1871. [4] Welte et al., Anal.Chem. 88 (2016) 8570. [5] Merchel et al., JRNCh, submitted. [6] A. Bischoff, pers.comm. (2021.) [7] Merchel, PhD thesis, (1998).

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  • Poster (Online presentation)
    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australien, 14.-19.11.2021, Sydney, Australien

Permalink: https://www.hzdr.de/publications/Publ-33385
Publ.-Id: 33385


¹⁰Be from commercial ⁹Be and ²⁷Al carrier solution – Some measurements

Merchel, S.; Braucher, R.; Lachner, J.; Rugel, G.

In the DREsden Acclerator Mass Spectrometry (DREAMS) chemistry laboratory, we see elevated but constant ¹⁰Be/⁹Be levels (1.2-2.0x10⁻¹⁵) when using a customised ⁹Be carrier [1]. In satellite and DREAMS laboratories unexperienced researchers and students are performing their own chemical separation, but the “human influence” is unlikely the sole explanation. Different levels of processing blanks as a function of the preparation laboratory are well-known also at other AMS facilities [2]. In our constant approach lowering processing blank levels for ¹⁰Be/⁹Be we have investigated two potential ¹⁰Be sources: ⁹Be and ²⁷Al carrier solutions.

Beryllium-9 carrier solutions are obvious ¹⁰Be sources and commercial and customised ones from minerals were already investigated earlier [3]. Inspired by numerous users asking for ⁹Be carrier analysis, we have compiled all (new) results from different AMS facilities. Remarkably, ¹⁰Be/⁹Be varies in the range of 1-10x10⁻¹⁵ from batch to batch (LOT) of the same company, very likely related to production date [4]. Currently, Australian Chemical Reagents and LGC provide carriers with the lowest intrinsic ¹⁰Be/⁹Be. For AMS users not affording a customised ⁹Be carrier, we advise buying larger quantities of commercial carriers to guarantee long-time low ¹⁰Be/⁹Be and saving precious AMS time from analysing new batches.

Another potential source for elevated and varying ¹⁰Be/⁹Be in processing blanks are Al carrier solutions (added to processing blanks) when performing ¹⁰Be/²⁶Al projects. According to [5] commercial aluminium contained ¹⁰Be in the range of 4-10x10⁷ ¹⁰Be atoms/g(Al). Nowadays, laboratories use 0.5-3.0 mg Al for processing blanks, which would yield into 4-10x10⁵ ¹⁰Be atoms/blank increasing the ¹⁰Be/⁹Be ratio to 6-10x10⁻¹⁵.

We asked in-situ dating researchers to provide their Al solutions. To differentiate between ¹⁰Be from Al and other sources (contamination in the chemistry laboratory or the ion source) we used a “basic standard-addition approach”: For each Al solution, two AMS targets containing ~300 µg ⁹Be and either 1 mg ²⁷Al or 3 mg ²⁷Al were prepared. After minimal chemistry (hydroxide precipitation, cation exchange, Be(OH)₂ precipitation, washing, drying, ignition, mixing with Nb) samples were measured at DREAMS.

Todays’ Al solutions are lower in ¹⁰Be compared to the Al investigated by [5]. None of our results is higher than 3.55x10⁻¹⁵, however, the two processing blanks without any Al have ¹⁰Be/⁹Be ratios of 1.2-1.7x10⁻¹⁵, which is in the same range as 12 out of 14 samples from ACROS, MERCK, ROTH and Traceselect, but 2-3 times higher than the machine blank. This means ~5x10⁴ ¹⁰Be atoms/sample are added from chemicals-consumables-materials or laboratory air-dust.
For more quantitative results about the ¹⁰Be concentration of Al carriers and to identify the main sources of the ¹⁰Be contribution for the processing blanks, additional experiments with larger amounts of Al (10-50 mg) and chemicals are needed.

Acknowledgments: Thanks to ASTER, DREAMS, Trondheim, VERA colleagues for ¹⁰Be data, and ANU, AWI, BOKU, CENIEH, CSFK, U Bratislava, U Jerusalem, U Potsdam colleagues for carrier solutions.

References: [1] Merchel et al., JRNCh (2013). [2] Wilcken et al., NIMB (2019). [3] Merchel et al., NIMB (2008). [4] Merchel et al., MethodsX (2021). [5] Middleton et al., NIMB (1994).

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    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 15.-19.11.2021, Sydney, Australien, 14.-19.11.2021, Sydney, Australien

Permalink: https://www.hzdr.de/publications/Publ-33384
Publ.-Id: 33384


Using in-situ cosmogenic 36Cl exposure dating of glacial erratics to establish a retreat chronology of the Iller Piedmont Glacier (Southern Germany)

Hildebrandt, D.; Hofmann, F.; Merchel, S.; Rugel, G.; Lachner, J.; Martschini, M.; Friedrich, A.

The dynamic behavior of glacial retreat following the globally diachronous Last Glacial Maximum (LGM) is poorly understood. In the Northern Alpine Foreland, multiple lobes of foreland glaciers produced a complex morpho-sedimentary record. While the reconstructed LGM ice extent is laterally constant in the west, it shows significant variations in the central and eastern parts. We explore how these geological differences relate to local climatic variability and global paleoclimate during a period of rapid climate change in the late Pleistocene.

In this study, we employ cosmogenic ³⁶Cl in limestone to constrain the in-situ exposure age of glacial erratics situated on moraine walls of the Iller Piedmont Glacier. We sampled erratic boulders from three moraine crests previously interpreted to represent the LGM and two post-LGM retreat stands. We measured ³⁶Cl/Cl and Cl-nat of seven samples from all three locations by applying routine chemistry protocols (Merchel et al., 2013) and isotope-dilution AMS measurements using a dedicated ion source for halogenides (Pavetich et al., 2014) at the DREsden AMS facility.

Preliminary results show that the sampled boulder surfaces provide internally consistent, reproducible, and geologically meaningful dates. Field investigations indicate that some of the erratic boulders were affected by chemical weathering, slope processes or human activities after their glacial deposition, thereby influencing the measured in-situ ³⁶Cl concentrations. In order to account for these complexities, we apply appropriate correction factors to obtain more accurate ages and discuss the related uncertainties.

Sample preparation of 14 additional samples was performed at the Laboratory for cosmogenic nuclide extraction at the University of Natural Resources and Life Sciences (BOKU) in Vienna. We will likely present ³⁶Cl/Cl and Cl-nat data of these additional samples measured at the Vienna Environmental Research Accelerator (VERA) at the time of the meeting. The exposure age data elucidate the spatio-temporal patterns of receding glaciers in the Northern Alpine Foreland, and place constraints on climate reconstructions for Central Europe during the late Pleistocene.

Acknowledgements:

We are grateful to Stephanie Neuhuber (BOKU Vienna) for providing access to her CN laboratory. Kathrin Strößner, Hagen Hoemann, Paul Herwegh, Kaja Schulz and Sami Akber (all LMU Munich) are thanked for assistance with sample preparation. This work was funded by DFG (German Science Foundation) grant FR 1673/15-1. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden–Rossendorf (HZDR) e. V., a member of the Helmholtz Association, supported by the HZDR Beamtime Proposal 20002195-ST. AMS measurements and sample preparation in Vienna are supported by the RADIATE project under the Grant Agreement 824096319 from the EU Research and Innovation programme HORIZON 2020 trough the Transnational Access grant 21002431-ST.

References:

Merchel et al., Quat. Geochron. 18 (2013) 54.
Pavetich et al., NIMB 329 (2014) 22.

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  • Poster (Online presentation)
    The 15th International Conference on Accelerator Mass Spectrometry (AMS-15), 14.-19.11.2021, Sydney, Australien

Permalink: https://www.hzdr.de/publications/Publ-33383
Publ.-Id: 33383


Relative cerebral blood volume reduction in hyperintense brain regions of glioma patients treated with proton radio(chemo)therapy

Witzmann, K.; Raschke, F.; Wesemann, T.; Appold, S.; Krause, M.; Linn, J.; Troost, E. G. C.

Introduction:

Adjuvant radio(chemo)therapy (RT) is part of the treatment of patients with primary brain tumors. A major challenge following radiotherapy is to distinguish between tumor recurrence and radiation-induced effects. Hyperintensities in T2-weighted (T2w) MRI are commonly observed after radiotherapy but are not specific to the underlying tissue changes. The value of advanced methods, such as perfusion MRI, has already been shown for differentiating between tumor and treatment effect [1,2]. The aim of this study was to evaluate changes of relative cerebral blood volume (rCBV) in areas of T2w-hyperintensities in order to establish an imaging biomarker differentiating between tumor and treatment effect.

Methods:

In a longitudinal study, anatomical and functional MRI data of glioma patients undergoing gross tumor resection followed by RT were collected. We analyzed a subset of this cohort, which consisted of 14 glioma patients (3 grade II, 8 grade III, 3 grade IV, average age 48.1y ± 13.5y) with tissue hyperintensities on T2w FLAIR images after proton beam irradiation. All MRI data were collected on a 3T Philips Ingenuity PET/MR scanner (Philips, Eindhoven, The Netherlands) using an 8 channel head coil and included anatomical T1w images [3D-GRE, TR/TE=10/3.7ms, FA=20°, voxel size 1×1×1mm3], contrast enhanced T1w images (CET1w) [3D Turbo Field Echo (TFE), TR/TE=8.2/3.7ms, FA=8°, voxel size 1×1×1mm3], 3D FLAIR images [TR/TE = 4800/293ms, TI = 1650ms, 2 averages, voxel size 0.49×0.49×0.5mm3, 360 slices], and dynamic susceptibility contrast (DSC) images using a PRESTO sequence [TR/TE=15/21ms, FA=7°, 60 dynamics, dynamic scan time=1.7s, voxel size 1.8×1.8×3.5mm3] with intravenous gadolinium contrast agent (0.1mol/kg, 4ml/s, 7s delay) followed by a saline flush (20ml, 4ml/s). The same dose of contrast agent was given as a pre-bolus for leakage correction of the DSC perfusion images. MRI scans were acquired prior to RT and post RT in three monthly intervals. In this analysis only the baseline data and the measurement of the latest follow-up time point (18.9 ± 8.2 months after RT) were considered.
To determine cerebral blood volume (CBV) with DSC, the signal time curves of the dynamic PRESTO measurements were converted to concentration time curves. CBV was calculated by the division of the area under the time curve determined by a gamma variate fit function with the arterial input function. CBV-maps were normalized to a normal appearing WM ROI receiving a radiation dose less than 1Gy resulting in the rCBV. The hyperintensity mask indicated on T2w images was determined by the ratio of follow-up and baseline FLAIR images which were registered non-linearly to each other with ANTs [3]. The area showing contrast enhancements in the follow-up measurement was identified by comparing CET1w and T1w images. Hyperintensity mask (HI), contrast enhancement mask (CE), planning computed tomography images (CTs), radiation dose, clinical target volume (CTV) and gross tumor volume (GTV) resp. tumor bed volume (TBV) contour were rigidly registered first to the T1w image and then to the CBV image using ANTs [3] . The region of interest (ROI) was defined based on the hyperintensity mask in the follow-up measurement excluding the GTV resp. TBV and the CE. Four patients did not show any contrast enhancement. The ROI was transferred to the baseline images to evaluate the same region in baseline and follow-up measurement. The rCBV distributions were evaluated comparing the histograms of follow-up and baseline measurement and the Kolmogorow-Smirnow (KS)-test was used to examine the similarity of the histograms. Additionally, the rCBV alterations were analyzed visually.

Results:

The KS-test revealed a significant inequality between follow-up and baseline histograms for all patients, which was expressed by a shift to lower rCBV values in the follow-up measurement (figure 2). Visual examination confirmed the impression of decreasing perfusion in the hyperintense areas, as shown for one patient in figure 1.

Discussion:

We found decreasing perfusion in the hyperintense areas which can be interpreted as treatment effect appearing after RT according to previous studies [4-6]. The baseline evaluation is more distorted by the vascular influence due to inaccuracies in registration and tissue deformation to the transmitted ROI. This can potentially lead to higher baseline perfusion values in some areas caused by grey matter (GM) or vessels. The baseline maps (figure 1B-D) show this effect of blood vessels to the rCBV in the ROI. Due to these factors, comparing mean rCBV values within the ROIs or voxel-based evaluation of the perfusion changes is compromised. Further work is now needed to correlate the observed perfusion changes with histological data.

Conclusion:

The combination of visual impression and histogram analysis showed a decreasing perfusion in the hyperintense areas. Quantitative evaluation requires the exclusion of the influence of the vessels as well as the consideration of tissue displacements. For further studies, the appearance of rCBV changes in areas depending on proximity to CE would be of high interest [7,8] as well as a dose-dependent evaluation.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB & SMRT 31st Annual Meeting, 07.-12.05.2022, London, United Kingdom
  • Poster
    Joint Annual Meeting ISMRM-ESMRMB & SMRT 31st Annual Meeting, 07.-12.05.2022, London, United Kingdom

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Publ.-Id: 33382


Domain wall damping in ultrathin nanostripes with Dzyaloshinskii-Moriya interaction

Volkov, O.; Pylypovskyi, O.; Kronast, F.; Abert, C.; Oliveros Mata, E. S.; Makushko, P.; Mawass, M.-A.; Kravchuk, V.; Sheka, D.; Faßbender, J.; Makarov, D.

Structural inversion symmetry breaking in low-dimensional magnetic systems determines their electronic and magnetic properties at interfaces [1,2]. Asymmetrically sandwiched magnetic films can provide strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interactions (DMI), which is necessary for prospective memory and logic devices based on chiral non-collinear magnetic textures, e.g. skyrmions [3,4], skyrmion bubbles and chiral domain walls (DWs) [5]. The device performance is determined by the static and dynamic micromagnetic parameters [6,7]. In particular, the speed of a DW-based racetrack memory is defined by both the strength of the external driving, e.g. magnetic field or spin-polarized current, and internal magnetic parameters, e.g. the DMI constant and damping parameter [6,7]. The necessity of having a strong DMI in asymmetrically sandwiched magnetic structures requires the utilization of ultrathin (in the range of 1 nm) magnetic films, which implies the polycrystalinity and compromized structural quality of the layer stack. Structural imperfections in addition to the spin-pumping mechanism [8,9], that arises due to the proximity of a ferromagnetic material with a heavy-metal, lead to a substantial enhancement of the magnetic damping parameter of ultrathin films compared to bulk. Accessing this parameter typically requires dynamic experiments on the motion of DWs in confined geometries, which are usually done in the creep regime due to the pronounced pinning.

Here, we demonstrate both experimentally and theoretically the presence of tilted DWs in statics in perpendicularly magnetized asymmetric //CrOx/Co/Pt layer stacks with surface-induced DMI, Fig. 1. We show that in such systems there are two possible theoretical mechanism for the appearance of titled DWs: (I) A unidirectional tilt could appear in equilibrium as a result of the competition between the DMI and additional in-plane easy-axis anisotropy, which breaks the symmetry of the magnetic texture and introduce tilts [10]. (II) A static DW tilt could appear due to the spatial variation of magnetic parameters, which introduce pinning centers for DWs. A moving DW can be trapped in a tilted state after the external driving field is off. Based on these theoretical approaches, we perform a statistical analysis of the DW tilt angles obtained in staticts after the external magnetic field used for the sample demagnetization was off. We found that the second approach corresponds better to the experimental observations and allows to determine self-consistently the range of DW damping parameters and DMI constants for the particular layer stack. Using two reference fields, which provide two characteristic tilt angles, allow us to retrieve the range of DMI strength mJ/m2 and DW damping parameters . The upper limit for the DMI constant agrees with an independent transport-based measurement giving mJ/m2, which further refines our estimate of the damping parameter . This value lies in a typical DW damping range for the Co-based asymmetrical layer stacks, that are obtained from dynamic experiments [11,12]. Thus, the combination of the proposed method with standard metrological techniques opens up opportunities for the quantification of both static and dynamic micromagnetic parameters based on static measurements of the DW morphology.
[1] A. Fert, N. Reyren, and V. Cros, Nature Reviews Materials 2, 17031 (2017).
[2] R. Wiesendanger, Nature Reviews Materials 1, 16044 (2016).
[3] A. N. Bogdanov and D. A. Yablonskiı̆, Zh. Eksp. Teor. Fiz. 95, 178 (1989).
[4] S. Woo, K. Litzius, B. Krüger, et al., Nature Materials 15, 501 (2016).
[5] S. Emori, U. Bauer, S.-M. Ahn, et al., Nature Materials 12, 611 (2013).
[6] C. Garg, S.-H. Yang, T. Phung, et al., Science Advances 3, e1602804 (2017).
[7] S. Parkin and S.-H. Yang, Nature Nanotechnology 10, 195 (2015).
[8] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, et al., Reviews of Modern Physics 77, 1375 (2005).
[9] A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, Physical Review Letters 101, 037207 (2008).
[10] O. V. Pylypovskyi, V. P. Kravchuk, O. M. Volkov, et al., Journal of Physics D: Applied Physics 53, 395003 (2020).
[11] J.-M. L. Beaujour, J. H. Lee, A. D. Kent, et al., Physical Review B 74 (2006).
[12] A. J. Schellekens, L. Deen, D. Wang, et al., Applied Physics Letters 102, 082405 (2013).

Keywords: Nanomagnetism; Dzyaloshinskii-Moriya interaction

  • Open Access Logo Lecture (Conference) (Online presentation)
    INTERMAG 2021, 26.-30.04.2021, Online, France

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Publ.-Id: 33381


OpenSource im Spannungsfeld akademischer und wirtschaftlicher Interessen

Schlegel, F.; Huste, T.; Juckeland, G.; Konrad, U.

Quelloffene Software ist aus der heutigen Wissenschaft nicht mehr wegzudenken und insbesondere im Hinblick auf die Sicherstellung der FAIR Prinzipien stellt sie eine hinreichende Bedingung dar. Die Verwendung von quelloffener Software ist jedoch durch eine Vielzahl von Besonderheiten geprägt, beispielsweise gibt es kein eindeutiges Finanzierungsmodel, wie es für kommerzielle Software in Form von Lizenzgebühren normalerweise der Fall ist. Die freie Verfügbarkeit der Software ermöglicht zudem völlig neue Konzepte in der Ausgestaltung der Beziehung zwischen den Anbietern und den Nutzern, sowie für die Organisation der Community. Hierdurch eröffnet sich ein Gestaltungsspielraum, welcher bisher nur bedingt durch die Forschungseinrichtungen genutzt wird, aber in sich ein enormes Potential für die Zukunft birgt.

Eine im Ingenieurwesen sehr erfolgreiche quelleoffene Software ist die C++-Bibliothek OpenFOAM1 zur Lösung partieller, nichtlinearer Differenzialgleichungen. OpenFOAM wird für eine Vielzahl von unterschiedlichen Anwendungen, wie beispielsweise in der Aerodynamik, in der Hydrodynamik oder in der Chemie- und Verfahrenstechnik eingesetzt. Die Anwender finden sich dabei nicht nur im akademischen Umfeld, sondern auch in der Industrie bei unterschiedlicher Firmen. In den letzten Jahrzehnten hat sich um OpenFOAM eine sehr aktive Community gebildet, mit zum Teil sehr unterschiedlichen Interessen und einem großen Konfliktpotential. Eine der wichtigsten Fragen beim Einsatz von OpenFOAM ist die langfristige und nachhaltige Softwareentwicklung, einerseits bei den Hauptentwicklern, aber vor allem auch bei den Wissenschaftlern. In einem typischen Arbeitsablauf wird zu Beginn einer Promotion ein Fork von OpenFOAM erstellt, in welchem der Doktorand seine Entwicklungen umsetzt. Häufig wird dieser Fork nach Abschluss der Promotion weder langfristig gepflegt, noch ins Release überführt und die Forschungsergebnisse gehen teilweise verloren. Die Ursachen hierfür sind vielfältig, u. a. mangelnde Finanzierung des notwendigen Re-Factorings und des langwierigen Diskussionsprozesses mit den Hauptentwicklern durch den Fördermittelgeber oder eine unzureichende Abbildung solcher Arbeiten in den Kennzahlen der wissenschaftlichen Arbeit und den Beschäftigungsmodellen des öffentlichen Dienstes.

Das Helmholtz-Zentrum Dresden-Rossendorf hat es sich zum Ziel gesetzt eine nachhaltige Softwareentwicklung für OpenFOAM gemeinsam mit der OpenFOAM Foundation anzustreben. Der geplante Beitrag soll die bisher gesammelten Erfahrungen des Helmholtz-Zentrum Dresden-Rossendorf im Umgang mit quelloffener Software am Beispiel von OpenFOAM präsentieren, welche aus dem intensiven Engagement als OpenFOAM Community Mitglied resultieren. Hierbei profitieren die Entwickler u. a. von den Möglichkeiten der Helmholtz-Gemeinschaft, insbesondere von den Helmholtz Federated IT Services (HIFIS)2. Der Vortrag zeigt einen möglichen Weg für eine wissenschaftliche Einrichtung mit einem guten Beispiel vorangehen und vernünftige Konzepte zu entwickeln quelloffene Software adäquat einzusetzen, nachhaltig weiterzuentwickeln, langfristig zu unterstützen und zu fördern. Ziel des Beitrages ist es Erfahrungen zu teilen, Probleme anzusprechen und eine Diskussion zur Beschreibung weiterer Wege anzuregen.

  • Lecture (Conference) (Online presentation)
    Software Engineering 2022, 21.-25.02.2022, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33380
Publ.-Id: 33380


Experimental confirmation of curvature-induced effects in magnetic nanosystems

Volkov, O.; Kakay, A.; Kronast, F.; Mawass, M.-A.; van den Brink, J.; Kravchuk, V.; Sheka, D.; Faßbender, J.; Makarov, D.

Curvilinear magnetism is the emerging field in micromagnetism which studies influences of external geometry and its topology on magnetic vector fields [1]. Much attention was paid to fundamental theoretical investigations of curvature-induced effects for local [2,3] and non-local magnetic interactions [4], which results in the prediction of various magnetochiral effects [2,5], topologically-induced magnetic patterns [5,6], stabilization of individual skyrmions [7,8] and skyrmion lattices [9] on curvilinear defects. Recently, we provided the very first experimental confirmation and quantitative assessment of the existence of the curvature-induced chiral interaction of exchange origin in a conventional soft ferromagnetic material [10]. In its turn, the interplay between the intrinsic and exchange-induced Dzyaloshinskii-Moriya interaction (DMI) paves the way to a mesoscale DMI [3], whose symmetry and strength depends both on the geometrical and material parameters of the magnetic system. Extending this concept we proposed a novel approach towards artificial magnetoelectric materials with helimagnetic nanohelices embedded in a piezoelectric matrix [11], where electric field could control magnetic states through the utilization of curvature-induced effects.

[1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016).
[2] Y. Gaididei et al., Phys. Rev. Lett. 112, 257203 (2014).
[3] O. Volkov et al., Sci. Rep. 8, 866 (2018).
[4] D. D. Sheka et al., Commun. Phys. 3, 128 (2020).
[5] V. P. Kravchuk et al., Phys. Rev. B 85, 144433 (2012).
[6] O. V. Pylypovskyi et al., Phys. Rev. Lett. 114, 197204 (2015).
[7] V. P. Kravchuk et al., Phys. Rev. B 94, 144402 (2016).
[8] O. V. Pylypovskyi et al., Physical Review Applied 10, 064057 (2018).
[9] V. P. Kravchuk et al., Phys. Rev. Lett. 120, 067201 (2018).
[10] O. M. Volkov et al., Phys. Rev. Lett. 123, 077201 (2019).
[11] O. M. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Keywords: Nanomagnetism; Curvilinear magnetism

  • Poster (Online presentation)
    717. WE-Heraeus-Seminar — Curvilinear Condensed Matter: Fundamentals and Applications, 24.-26.06.2021, Online, Germany

Permalink: https://www.hzdr.de/publications/Publ-33378
Publ.-Id: 33378


RevCAR platform as a combinatorial approach for targeting acute myeloid leukemia

Rodrigues Loureiro, L. R.; González Soto, K. E.; Kittel-Boselli, E.; Hoffmann, A.; Bergmann, R.; Arndt, C.; Mitwasi, N.; Kegler, A.; Bartsch, T.; Berndt, N.; Altmann, H.; Fasslrinner, F.; Bornhäuser, M.; Bachmann, M.; Feldmann, A.

Background:

In the past years, the treatment of acute myeloid leukemia (AML) has been significantly shifted towards the development of targeted approaches. Nonetheless, clinical translation of novel immunotherapeutic strategies such as chimeric antigen receptor (CAR) T-cells in AML is still at an early stage. Given the heterogeneity of such disease, major challenges include immune escape and disease relapse, which demand for further improvements in the CAR design. To overcome such hurdles, we have invented the switchable, flexible and programmable adaptor RevCAR platform. This consists of T-cells engineered with RevCARs that are primarily inactive as they express an extracellular short peptide epitope incapable of recognizing surface antigens. RevCAR T-cells can be redirected to tumor antigens and controlled by bispecific antibodies cross-linking RevCAR T- and tumor cells resulting in tumor lysis. Remarkably, the RevCAR platform enables combinatorial tumor targeting following Boolean logic gates in which two separate RevCARs with different specificities can be simultaneously expressed and used to accomplish dual gated targeting of prominent AML antigens such as CD33 and CD123. We herein show for the first time the applicability of the RevCAR platform to target myeloid malignancies such as AML.

Methods:

Binding, functionality and proof-of-concept for combinatorial tumor targeting using the RevCAR system was assessed using both in vitro and in vivo models in different settings. For that, flow cytometry-based, cytokine release and cytotoxicity assays were performed using established AML cell lines or patient-derived material.

Results:

We have proven that AML cell lines as well as patient-derived AML blasts could be efficiently killed by redirected RevCAR T-cells targeting CD33 and CD123 in a flexible manner. Furthermore, by targeting both antigens, an AND gate logic targeting could be achieved using the RevCAR platform. This is a particular important approach to overcome existing or treatment related tumor escape variants and to tackle AML cancer heterogeneity.

Conclusions:

These accomplishments validate the preclinical versatility and controllability of the RevCAR platform embedded in one single system thereby paving the way for an improved and personalized immunotherapy of AML patients.

  • Lecture (Conference) (Online presentation)
    World Immunotherapy Council´s 4th Young Investigator Symposium (WIC), 10.11.2021, Washington, USA

Permalink: https://www.hzdr.de/publications/Publ-33377
Publ.-Id: 33377


Influence of surface activation on the microporosity of PE-CVD and PE-ALD SiOx thin films on PDMS

Hoppe, C.; Mitschker, F.; Mai, L.; Liedke, M. O.; de Los Arcos, T.; Awakowicz, P.; Devi, A.; Elsherif, A. G. A.; Butterling, M.; Wagner, A.; Grundmeier, G.

The microporosity, structure and permeability of SiOx thin films deposited by microwave plasma enhanced chemical vapour deposition and by plasma-enhanced atomic layer deposition on PDMS substrates were investigated by positron annihilation spectroscopy and complementary techniques. The chemical composition and morphology were analysed by X-ray photoelectron spectroscopy, polarization modulated-infrared reflection-absorption spectroscopy, time of flight spectroscopy and atomic force microscopy. The SiOx films were deposited onto spin-coated PDMS substrates, which were exposed to an oxygen plasma prior to thin film deposition. A correlation between the oxygen fluence during the oxygen plasma treatment and the microporosity of bth PE-CVD and PE-ALD SiOx films could be established. It was observed that a longer exposure to the oxygen plasma treatment resulted in formation of a SiOx-like surface near region of the PDMS film. In comparison to the as spin-coated PDMS surface, the oxidised surface near region led to an overall decrease in micropore density and to a shift towards smaller pore sizes within the deposited SiOx films.

Keywords: positron annihilation spectroscopy; positron annihilation lifetime spectroscopy; porosity; SiOx; plasma enhanced chemical vapour deposition; plasma-enhanced atomic layer deposition

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Permalink: https://www.hzdr.de/publications/Publ-33376
Publ.-Id: 33376


Curvature-induced effects in magnetic nanosystems

Volkov, O.; Sheka, D.; Kravchuk, V.; Rößler, U.; Faßbender, J.; Makarov, D.

Curvilinear magnetic objects are in focus of intensive research due to the possibility to obtain new
fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. In
geometrically-broken magnetic objects all energy functionals, that contains spatial derivatives, e.g.
exchange, magnetostatic and intrinsic Dzyaloshinskii-Moriya (DMI) interactions, are reshaping in a
way of appearance additional curvature-induced chiral and anisotropy terms. These novel chiral
magnetic responses arise in the physical space, by introducing bends and twists to magnetic
architectures even of conventional materials. We address both experimentally and theoretically the
appearance of curvature-induced exchange effects in parabolic nanostripes with different
geometrical parameters [2]. We show that a pinning of transversal domain wall at the parabolic apex
is originated due to the presence of local curvature-induced DMI that creates a subsequent pinning
potential. Measuring the depinning field enables to quantify the effective exchange-driven DMI
interaction constant. In its turn, the interplay between the intrinsic and exchange-induced DMI
paves the way to a mesoscale DMI, whose symmetry and strength depend both on the geometrical
and material parameters [3]. Developing this concept we propose a novel approach towards
artificial ME materials with helimagnetic nanohelices embedded in a piezoelectric matrix [4]. By
applying an electric field, small geometrical changes of pitch and radius could lead to the phase
transition from a homogeneously magnetized state (full average magnetic moment) to a periodical
one (zero average magnetic moment).

[1] R. Streubel et. al., J. Phys. D: Appl. Phys. 49,363001 (2016).
[2] O. Volkov et al.. Phys. Rev. Lett. 123, 077201 (2019).
[3] O. Volkov et al., Sci. Rep. 8, 866 (2018).
[4] O. Volkov et al., J. Phys. D: Appl. Phys. 52, 345001 (2019).

Keywords: Nanomagnetism; Curvilinear magnetism

  • Lecture (Conference) (Online presentation)
    APS March Meeting 2021, 15.-19.03.2021, Online, USA

Permalink: https://www.hzdr.de/publications/Publ-33375
Publ.-Id: 33375


KupferDigital Digital – Datenökosystem für die digitale Material- entwicklung auf Basis Ontologie-basierter digitaler Repräsentationen von Kupfer und Kupferlegierungen

Eisenbart, M.; Weber, M.; Wenige, L.; van den Boogaart, K. G.; Klengel, S.; Skrotzki, B.; Tikana, L.; Hupperz, M.; Füting, M.

Mit der Initiative MaterialDigital fördert das BMBF die Digitalisierung der Materialwissen-
schaft und Werkstoff technik in Deutschland. In diesem Rahmen fungiert die Plattform
MaterialDigital als Anlaufstelle für alle Interessenten und koordiniert die Aktivitäten zu
Digitalisierung in der Werkstoff welt. Mit dem im März 2021 gestarteten Projekt KupferDigital
ist nun auch der Werkstoff Kupfer ist bei der Initiative Plattform MaterialDigital vertreten. Das
Ziel des Projektes ist es, den Kupferlebenszyklus von der Erzgewinnung über die Material-
entwicklung und Herstellung sowie des Produktlebens bis hin zum Recycling digital zu
repräsentieren. Als Basis der Digitalisierung dienen hierzu Ontologien, die die digitale Material-
und Prozessbeschreibung einheitlich ermöglichen sollen und auch im größeren Zusammenhang
der Plattform MaterialDigital als gemeinsamer Standard entwickelt werden sollen.
Entstehen soll ein Datenökosystem, in dem der Datenaustausch über die verschiedenen
Instanzen des Lebenszyklus hinweg ermöglicht werden soll. Damit kann die Material- und
Produktentwicklung im eigenen Unternehmen Aspekte aus den anderen Stationen des
Lebenszyklus berücksichtigen und zum Beispiel Aspekte der Nachhaltigkeit berücksichtigen.

Keywords: Ontology; Copper Life Cycle

  • Poster
    Kupfer-Symposium 2021, 24.-25.11.2021, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33374
Publ.-Id: 33374


Fundamentals of curvilinear ferromagnetism: statics and dynamics of geometrically curved wires and narrow ribbons

Sheka, D.; Pylypovskyi, O.; Volkov, O.; Yershov, K.; Kravchuk, V. P.; Makarov, D.

Low-dimensional magnetic architectures including wires and thin films are key enablers of prospective ultrafast and energy efficient memory, logic and sensor devices relying on spin-orbitronic and magnonic concepts. Curvilinear magnetism emerged as a novel approach in material science, which allows tailoring of the fundamental anisotropic and chiral responses relying on the geometrical curvature of magnetic architectures. Much attention is dedicated to magnetic wires of Möbius, helical or DNA-like double helical shapes, which act as prototypical objects for the exploration of the fundamentals of curvilinear magnetism. Although there is a bulk number of original publications covering fabrication, characterization and theory of magnetic wires, there is no comprehensive review of the theoretical framework of how to describe these architectures. Here, we summarize theoretical activities on the topic of curvilinear magnetic wires and narrow nanoribbons, providing a systematic review of the emergent interactions and novel physical effects caused by the curvature. We discuss prospective research directions of curvilinear spintronics and spin-orbitronics, outline the fundamental framework for curvilinear magnonics and introduce mechanically flexible curvilinear architectures for soft robotics.

Keywords: curvilinear magnetism; nanowires; ribbons

Permalink: https://www.hzdr.de/publications/Publ-33373
Publ.-Id: 33373


Metal Oxides

Scheinost, A.; Singh, B.

Oxide minerals (include oxides, hydroxides, oxyhydroxides and hydrated oxides) are primary and secondary minerals of Si, Fe, Mn, Al and Ti. Secondary oxides, particularly of Fe, Al and Mn, are perhaps the most reactive and important components in many soils due to their high specific surface area and strong sorption capacity for many essential and potentially toxic elements. Iron and Mn oxides also play key roles in many redox reactions and have major influence on the transformation and availability of organic and inorganic contaminants in soils. This chapter provides an overview of the oxide minerals in soils, with an emphasis on their structure and composition, environmental conditions for their formation and their properties.

Keywords: Goethite; Hematite; ferrihydrite; gibbsite; quartz; redox; adsorption; secondary minerals

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Permalink: https://www.hzdr.de/publications/Publ-33372
Publ.-Id: 33372


Measurement of magnetic fringe fields from a proton pencil beam scanning nozzle causing MR image ghosting artefacts during in-beam MR imaging

Semioshkina, E.; Oborn, B.; Hoffmann, A. L.

INTRODUCTION:

Proton therapy (PT) produces highly conformal dose distributions with steep gradients at the target boundaries due to the finite range of protons. This reduces normal-tissue doses, particularly at the distal side of the tumor where the Bragg peak is located. However, the targeting precision of PT is compromised by a lack of image guidance: imaging modalities in treatment rooms of PT facilities are often limited to X-ray based on-board 2D kV or 3D cone-beam CT imaging. The integration of fast real-time MR imaging could significantly improve on-board imaging and therefore increase the targeting accuracy of PT, especially for moving tumors [1].
However, a full integration of MRI and PT at the treatment isocenter is technically challenging due to the electromagnetic interaction between both systems. Although a first proof-of-concept for in-beam MRI has proven successful in combination with a static proton research beamline [2], the combination of a research prototype in-beam MRI system with a beamline featuring an actively scanned proton beam (figure 1) has proven problematic. MR images acquired during proton pencil beam scanning (PBS) dose delivery were blurred by coherent ghosting artefacts due to dynamic magnetic fringe fields produced by nearby beam steering magnets overlapping with the B0 field of the MR scanner (figure 2) [3]. One way to eliminate these artifacts could be passive magnetic shielding of the beam steering magnets. This would lead to decoupling the magnetic fields of the MR scanner and the PBS nozzle. To be able to design an optimal shielding solution, a detailed understanding of the magnitude of the magnetic fringe fields produced by the PBS nozzle is mandatory. The aim of this study was to measure the magnetic fringe fields produced by the PBS nozzle. The experimental data will be used to help optimize and validate a finite element model (FEM) of the PBS nozzle that is under development.
METHODS:
A proton beam of therapeutic quality was generated by an isochronous cyclotron (C230, IBA SA, Louvain-la-Neuve, Belgium). The proton PBS nozzle of a horizontal research beamline included two sets of dipole magnets to scan the beam in horizontal (X) and vertical (Y) direction across a target volume during dose delivery. A fluxgate magnetometer (Mag649-200, Metrolab Technology SA, Geneva, Switzerland) was used to measure the magnitude of the magnetic fringe fields produced by the beam scanning magnets. It was positioned on a mobile tripod in front of the PBS nozzle at 13 locations as demonstrated in figure 3 at the height of the central beam axis (i.e. 126 cm above floor level). The delivery of two dose spot maps was emulated by energizing the magnets of the PBS beamline for a proton beam of 220 MeV, but no beam was released from the cyclotron in order to prevent radiation damage to the magnetometer. A beam energy of 220 MeV was chosen to achieve the maximum magnitude of magnetic fringe fields produced by the beamline magnets, and thus represent the worst-case scenario. Each dose spot map included a single dose point of 4500 monitor units (MUs) irradiated at a dose rate of approximately 155.2 MU/s. The X scanning magnets were energized to emulate the delivery of two dose spots to extreme positions at (X = -20 cm, Y = 0 cm) and (X = 20 cm, Y = 0 cm) relative to the beam isocenter. This experiment was repeated three times. The Y scanning magnets were not energized, as their fringe fields were previously shown not to affect the MR image quality [3].
RESULTS:
The maximum magnitude of the magnetic fringe field of scanning magnets was measured on the central beam axis at PBS isocenter (Figure 4). The fringe field magnitude varied from 2 µT to 6 µT over the volume where the in-beam MR scanner will be placed. A slight asymmetry in the measured values along the lateral direction (i.e. perpendicular to the central beam axis) was observed (see figure 4a).

DISCUSSION:

The resolution and the measuring range of the magnetometer are well suited to perform the measurements in the volume of high interest, i.e. the volume where the in-beam MR scanner is positioned. Even the 1 µT changes in the magnetic field, e.g., the asymmetry along the lateral direction, were detected. The asymmetric measurement results from the asymmetric design of the PBS nozzle. However, the resolution of 0.5 µT did not allow measurements in lower magnetic fields and the magnetometer became oversaturated in the regions of higher magnetic field strengths. Further measurements outside the volume in which the MR scanner is positioned, e.g., in the immediate proximity of the PBS nozzle where the magnetic field strength is largest, require a magnetometer with an extended measuring range and resolution.

CONCLUSION:

The magnitude of the magnetic fringe field produced by the PBS nozzle was successfully measured experimentally for two dose spot maps at extreme spot scanning positions. The valuable measurement data will be used to optimize and validate the FEM model of the PBS nozzle. More measurements using different beam energies, dose spot positions and measurement positions of the magnetometer are needed to complete the validation of the FEM.

  • Contribution to proceedings
    Joint Annual Meeting ISMRM-ESMRMB, 07.-12.05.2022, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-33371
Publ.-Id: 33371


Application of multi-edge HERFD-XAS to assess the uranium valence electronic structure in potassium uranate (KUO3)

Bes, R.; Leinders, G.; Kvashnina, K.

The uranium valence electronic structure in the prototypical undistorted perovskite
KUO3 is reported on the basis of a comprehensive experimental study using multi-
edge HERFD-XAS and relativistic quantum chemistry calculations based on DFT.
Very good agreement is obtained between theory and experiments, including the con-
firmation of previously reported Laporte forbidden f-f transitions and X-ray photo-
electron spectroscopic measurements. Many spectral features are clearly identified in
the probed U-f, U-p and U-d states and the contribution of the O-p states in those fea-
tures could be assessed. The octahedral crystal field strength, 10Dq, was found to be 6.6(1.5) eV and 6.9(4) eV from experiment and calculations respectively. Calculated
electron binding energies down to U-4f states are also reported.

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Permalink: https://www.hzdr.de/publications/Publ-33370
Publ.-Id: 33370


Effective coordination numbers from EXAFS: General approaches for dioxides

Romanchuk, A.; Trigub, A.; Plakhova, T.; Kuzenkova, A.; Svetogorov, R.; Kvashnina, K.; Kalmykov, S.

EXAFS is one of the comprehensive usable method to characterize structures of various
materials including radioactive and nuclear materials. Unceasing discussions about the interpretation of
EXAFS results for actinides nanoparticles (NPs) or colloids remain during the last decates. In this paper,
the new experimental data for PuO2 and CeO2 NPs with different average sizes are compared with
published data on AnO2 NPs that shed the light on the best fit and interpretation of the structural data.
Structurally PuO2, CeO2, ThO2, and UO2 NPs demonstrate similar behavior. Only ThO2 NPs have a
more disordered and even partly amorphous structure that results in EXAFS characteristics. The
proposed new core-shell model for NPs with calculated effective coordination number perfectly fits the
results on variations in Me-Me shell with the decrease of NPs size.

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Permalink: https://www.hzdr.de/publications/Publ-33369
Publ.-Id: 33369


Geographical data analysis in the historical research

Mertel, A.

Část interdisciplinárních studií v sociálních vědách se v posledních letech zastřešuje termíny jako "Cultural Analytics", "Cliodynamics" nebo "Digital (Geo) Humanities". Soustřeďují pozornost na otázky digitalizace, sdílení a popisu (metadata) zdrojů, datové analýzy a vizualizace ve vědeckých oblastech, kterým jsou tradičně vlastní spíše kvalitativní metody, což platí v neposlední řadě i pro historický výzkum. Úkolem (geografické) datové analýzy je obecně snaha transformovat data do podoby, ze které je možné získat novou vědomost. Přestože je dnes proces datové analýzy relativně standardizovaný, prostředí historického výzkumu má několik specifik, k nimž je třeba přihlížet. Prezentace se soustředí na tyto specifika v kontextu geografické datové analýzy, jež jsou přítomna v procesu sběru a zpracování dat, volby a implementace metodologie a také interpretace a validace výstupů.

Keywords: spatial data analysis; historical science; data uncertainty; geocoding; source modeling; least cost analysis; environmental modeling

  • Invited lecture (Conferences)
    LINDAT CLARIAH-CZ Talk, 12.11.2021, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-33368
Publ.-Id: 33368


Symmetry and curvature effects on spin waves in vortex-state hexagonal nanotubes

Körber, L.; Zimmermann, M.; Wintz, S.; Finizio, S.; Kronseder, M.; Bougeard, D.; Dirnberger, F.; Weigand, M.; Raabe, J.; Otálora, J. A.; Schultheiß, H.; Josten, E.; Lindner, J.; Kézsmárki, I.; Back, C. H.; Kakay, A.

Analytic and numerical studies on curved magnetic nano-objects predict numerous exciting effects that can be referred to as magneto-chiral effects, which do not originate from intrinsic Dzyaloshinskii–Moriya interaction or interface-induced anisotropies. In constrast, these chiral effects stem from isotropic exchange or dipole-dipole interaction, present in all magnetic materials, which acquire asymmetric contributions in case of curved geometry of the specimen. As a result, for example, the spin-wave dispersion in round magnetic nanotubes becomes asymmetric, namely spin waves of the same frequency propagating in opposite directions along the nanotube exhibit different wavelenghts. Here, using time-resolved scanning transmission X-ray microscopy experiments, standard micromagntic simulations and a dynamic-matrix approach, we show that the spin-wave spectrum undergoes additional drastic changes when transitioning from a continuous to a discrete rotational symmetry, i.e. from round to hexagonal nanotubes, which are much easier to fabricate. The polygonal shape introduces localization of the modes both to the sharp, highly curved corners and flat edges. Moreover, due to the discrete rotational symmetry, the degenerate nature of the modes with azimuthal wave vectors known from round tubes is partly lifted, resulting in singlet and duplet modes. For comparison with our experiments, we calculate the microwave absorption from the numerically obtained mode profiles which shows that a dedicated antenna design is paramount for magnonic applications in 3D nano-structures. To our knowledge these are the first experiments directly showing real space spin-wave propagation in 3D nano objects.

Keywords: spin wave; dispersion; curvature; micromagnetic modeling; hexagonal; symmetry; STXM

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Permalink: https://www.hzdr.de/publications/Publ-33367
Publ.-Id: 33367


Numerical reverse engineering of general spin-wave dispersions: Bridge between numerics and analytics using a dynamic-matrix approach

Körber, L.; Kakay, A.

Modern problems in magnetization dynamics require more and more the numerical determination of the spin-wave spectra and -dispersion in magnetic systems where analytic theories are not yet available. Micromagnetic simulations can be used to compute the spatial mode profiles and oscillation frequencies of spin-waves in magnetic system with almost arbitrary geometry and different magnetic interactions. Although numerical approaches are very versatile, they often do not give the same insight and physical understanding as analytical theories. For example, it is not always possible to decide whether a certain feature (such as dispersion asymmetry, for example) is governed by one magnetic interaction or the other. Moreover, since numerical approaches typically yield the normal modes of the system, it is not always feasible to disentangle hybridized modes. In this manuscript, we build a bridge between numerics and analytics by presenting a methodology to calculate the individual contributions to general spin-wave dispersions in a fully numerical manner. We discuss the general form of any spin-wave dispersion in terms of the effective (stiffness) fields produced by the modes. Based on a special type of micromagnetic simulation, the numerical dynamic-matrix approach, we show how to calculate each stiffness field in the respective dispersion law, separately for each magnetic interaction. In particular, it becomes possible to disentangle contributions of different magnetic interactions to the dispersion asymmetry in systems where non-reciprocity is present. At the same time, dipolar-hybridized modes can be easily disentangled. Since this methodology is independent of the geometry or the involved magnetic interactions at hand, we believe it is attractive for experimental and theoretical studies of magnetic systems where there are no analytics available yet, but also to aid the development of new analytical theories.

Keywords: spin wave; Micromagnetic simulations; theory; dispersion; dynamic-matrix approach; normal modes; hybridization; numerics

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Publ.-Id: 33366


Data for: Heterogeneous sorption of radionuclides predicted by crystal surface nanoroughness

Yuan, T.; Schymura, S.; Bollermann, T.; Molodtsov, K.; Chekhonin, P.; Schmidt, M.; Stumpf, T.; Fischer, C.

Reactive transport modeling (RTM) is an essential tool for the prediction of contaminants’ behavior in the bio- and geosphere. However, RTM of sorption reactions is constrained by the reactive surface site assessment. The reactive site density variability of the crystal surface nanotopography provides an “energetic landscape”, responsible for heterogeneous sorption efficiency, not covered in current RTM approaches.  Here, we study the spatially heterogeneous sorption behavior of Eu(III), as an analogue to trivalent actinides, on a polycrystalline nanotopographic calcite surface and quantify the sorption efficiency as a function of surface nanoroughness. Based on experimental data from micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS), vertical scanning interferometry, and electron back-scattering diffraction (EBSD), we parameterize a surface complexation model (SCM) using surface nanotopography data. The validation of the quantitatively predicted spatial sorption heterogeneity suggests that retention reactions can be considerably influenced by nanotopographic surface features. Our study presents a way to implement heterogeneous surface reactivity into a predictive SCM for enhanced prediction of radionuclide retention.

Keywords: Sorption reactions; Crystal surface reactivity; µTRLFS; Surface complexation modeling; Radionuclide migration

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Permalink: https://www.hzdr.de/publications/Publ-33364
Publ.-Id: 33364


Data publication: Nanoindentation response of ion-irradiated Fe, Fe-Cr alloys and ferritic-martensitic steel Eurofer 97: The effect of ion energy

Das, A.; Altstadt, E.; Kaden, C.; Kapoor, G.; Akhmadaliev, S.; Bergner, F.

The dataset consists of inputs from ion irradiation experiments, nanoindentation and empirical modeling results for Fe (G379), ferrritic Fe-9Cr (G385), martensitic Fe-9Cr (L252) and Eurofer 97 steel. The dataset also includes the basic characterization of microstructure.

Keywords: iron; Fe-Cr alloy; ferritic-martensitic steel; ion irradiation; displacement damage; nanoindentation; irradiation hardeníng; indentation size effect

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Permalink: https://www.hzdr.de/publications/Publ-33362
Publ.-Id: 33362


A Small Step, a Giant Leap: Somatic Hypermutation of a Single Amino Acid Leads to Anti-La Autoreactivity

Bartsch, T.; Arndt, C.; Rodrigues Loureiro, L. R.; Kegler, A.; Puentes-Cala, E.; Soto, J. A.; Kurien, B. T.; Feldmann, A.; Berndt, N.; Bachmann, M.

The anti-La mab 312B, which was established by hybridoma technology from human-La transgenic mice after adoptive transfer of anti-human La T cells, immunoprecipitates both native eukaryotic human and murine La protein. Therefore, it represents a true anti-La autoantibody. During maturation, the anti-La mab 312B acquired somatic hypermutations (SHMs) which resulted in the replacement of four aa in the complementarity determining regions (CDR) and seven aa in the framework regions. The recombinant derivative of the anti-La mab 312B in which all the SHMs were corrected to the germline sequence failed to recognize the La antigen. We therefore wanted to learn which SHM(s) is (are) responsible for anti-La autoreactivity. Humanization of the 312B ab by grafting its CDR regions to a human Ig backbone confirms that the CDR sequences are mainly responsible for anti-La autoreactivity. Finally, we identified that a single amino acid replacement (D > Y) in the germline sequence of the CDR3 region of the heavy chain of the anti-La mab 312B is sufficient for anti-La autoreactivity.

  • Open Access Logo International Journal of Molecular Sciences 22(2021)21, 12046
    Online First (2021) DOI: 10.3390/ijms222112046

Permalink: https://www.hzdr.de/publications/Publ-33361
Publ.-Id: 33361


Characterizing material liberation of multi-material lightweight structures from shredding experiments and finite element simulations

Heibeck, M.; Rudolph, M.; Modler, N.; Reuter, M.; Filippatos, A.

Most products in automotive, aerospace, and household appliance industry are multi-material structures. Materials are connected through a variety of joining techniques with the aim of optimizing performance during production and operation phase. However, during recycling in the end-of-life phase, different materials combined in multi-material structures need to be liberated, e.g. disconnected, and separated again to enable high material recoveries. Typical recycling approaches use shredding technologies to liberate materials. Efficient material liberation contributes to achieving high recycling rates for end-of-life products set by the European Union, thereby reducing the need for primary resource extraction and leading to a more sustainable development.

To characterize material liberation, we conducted an experimental shredding study with multi-material lightweight structures typical for automotive A-frames consisting of steel and composite materials, which were shredded in two sequences in a pilot rotary shear. We characterized feed and resulting progeny particles through a set of quantitative and qualitative metrics, thereby tracking changes in joint characteristics, material composition and particle sizes over the course of two processing steps. We found that material liberation is dependent on many design and shredding parameters. Our characterization approach for feed and progeny particles allows for linking design parameters to liberation behaviour. Due to high variability of design and shredding parameters experimental data acquisition is effortful. Therefore, we present an outlook on first results of our physics-based, numerical simulation model using Finite Element Method. Once validated, shredding simulations of many design configurations shall inform the designer about the liberation behaviour of a multi-material structure, such as the A-frame specimens.

Keywords: Recycling; Shredding; Multi-material design; Material liberation; Joint characterization; Composites; Finite Element Method

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Permalink: https://www.hzdr.de/publications/Publ-33360
Publ.-Id: 33360


Two-dimensional materials under ion irradiation: from defect production to structure and property engineering

Ghorbani Asl, M.; Kretschmer, S.; Krasheninnikov, A.

Similar to their bulk 3D counterparts, the properties of two-dimensional
(2D) materials can be tuned by controllable introduction of impurities
and defects using beams of energetic ions, which requires
complete microscopic understanding of their response to ion irradiation.
The behavior of 2D materials under ion beam is also interesting in the context of their applications in radiation-hostile environments such as cosmic space. While irradiation effects in 3D systems are well understood, a growing body of experimental facts indicate that many concepts of energetic particle-solid interaction developed for 3D materials are not applicable to 2D systems due to their very geometry, or require substantial modifications. In this Chapter, we discuss at length the response of 2D materials to ion irradiation in different regimes with the main focus on the role of reduced dimensionality. We illustrate the differences between the impact of ions on 3D and 2D materials by examples taken from the recent theoretical and experimental studies on the response of 2D materials to ion irradiation and outline general trends in their behavior under irradiation. Finally, we discuss how ion beams can be used to engineer the structure and properties of 2D materials.

Keywords: Two-dimensional materials; ion irradiation; defect; engineering

Related publications

  • Book chapter
    Rafik Addou and Luigi Colombo: Defects in Two-Dimensional Materials, Amsterdam, Netherlands: Elsevier, 2022, 9780128202920, 259-301
    DOI: 10.1016/B978-0-12-820292-0.00015-X

Permalink: https://www.hzdr.de/publications/Publ-33359
Publ.-Id: 33359


Chelators for treatment of iron and copper overload: Shift from low-molecular-weight compounds to polymers

Hruby, M.; Santana Martinez, I. I.; Stephan, H.; Pouckova, P.; Benes, J.; Stepanek, P.

Iron and copper are essential micronutrients needed for the proper function of every cell. However, in excessive amounts these elements are toxic as they may cause oxidative stress resulting in damage of liver and other organs. This may happen due to poisoning, as side effect of thalassemia infusion thera-py or due to hereditary diseases hemochromatosis or Wilson´s disease. The current golden standard of therapy of iron and copper overload is the use of low-molecular-weight chelators of these elements. However, these agents suffer from severe side effects, are often expensive and possess unfavourable pharmacokinetics, which is all limiting useability of such therapy. The emerging concept are poly-mer-supported iron- and copper-chelating therapeutics, either for parenteral or oral use, which show vivid potential to keep therapeutic efficacy of low-molecular-weight agents while avoiding their draw-backs and especially side effects. Critical evaluation of this new perspective polymer approach is the purpose of this review article.

Keywords: iron; copper; polymer; chelator; Wilson's disease; hemochromatosis

Permalink: https://www.hzdr.de/publications/Publ-33358
Publ.-Id: 33358


SOLSTICE - Na-Zn molten salt batteries

Duczek, C.; Lee, J.; Monrrabal Marquez, G.; Weber, N.; Weier, T.

The first results of the EU project SOLSTICE will be presented.

  • Communication & Media Relations
    Battery Innovation Days (online Messestand) 23.11.2021

Permalink: https://www.hzdr.de/publications/Publ-33357
Publ.-Id: 33357


SOLSTICE - Na-Zn molten salt batteries

Weber, N.; Heinz, M.; Lee, J.; Weier, T.

The talk gives a very short overview on the EU project SOLSTICE.

  • Invited lecture (Conferences) (Online presentation)
    Horizon 2020 Batteries Projects clustering event, 17.-18.11.2021, Brüssel, Belgien

Permalink: https://www.hzdr.de/publications/Publ-33356
Publ.-Id: 33356


Liberation and separation of valuable components from LED modules: presentation of two innovative approaches

Balinski, A.; Recksiek, V.; Stoll, M.; Christesen, C. S.; Stelter, M.

The rapid development of light-emitting-diode (LED) technology is attributed to its superiority over light sources of earlier generations. Although LED lamps, compared to compact fluorescent lamps, are considered less harmful to the environment, there is still no efficient solution to deal with them at the end of their lifecycle. The first part of the study provides a detailed characterisation of LED lamps, focusing on their most interesting component: the LED module. LED packages attached to the module are highly enriched with Ga, In, Pd, Ag, Au, Sr, Y, Ce, Eu, Gd, and Lu, with the content of each element varying greatly depending on the LED technology. In the second part of this research, two new approaches for liberation and concentration of valuable components from LED modules are presented and compared: a chemical route and a thermal route. The chemical treatment leads to a highly selective separation of LED chips and encapsulation. Enrichment factors up to about 125 are achieved, and a concentrate is obtained containing approximately 14 wt% of the aforementioned valuable components. However, the process requires aromatic solvents, which are viewed as toxic. The thermal treatment results in separation of the aluminium heat sink from all other components of the LED module. Enrichment is approximately ten times lower, but the approach is technically feasible.

Keywords: LED lamps; recycling; waste electrical and electronic equipment; gallium; precious metals; rare earth elements

Permalink: https://www.hzdr.de/publications/Publ-33355
Publ.-Id: 33355


Germanium as an ultrabroadband THz material

Helm, M.; Singh, A.; Pashkin, O.; Winnerl, S.; Beckh, C.; Sulzer, P.; Leitenstorfer, A.; Schneider, H.

Germanium, as an elemental semiconductor, has no Reststrahlen band and is thus suited as a broadband THz material, even for THz generation. The drawback of its long carrier lifetime due to the indirect band gap can be remedied through ion implantation, and the relatively small size of the gap allows excitation with fiber lasers in the telecom range. We demonstrate THz emission from Ge photoconductive antennas reaching as far as 70 THz.

Keywords: germanium; THz; photoconductive antenna; braodband

  • Invited lecture (Conferences) (Online presentation)
    RJUSE TeraTech 2021, 01.-04.11.2021, Sendai, Japan
  • Contribution to proceedings
    RJUSE TeraTech 2021, 01.-04.11.2021, Sendai, Japan
    RJUSE TeraTech 2021 Conference Digest

Permalink: https://www.hzdr.de/publications/Publ-33354
Publ.-Id: 33354


Data publication: How 5f electron polarizability drives covalency and selectivity in actinide N-donor complexes

Köhler, L.; Patzschke, M.; Schmidt, M.; Stumpf, T.; März, J.

Diese Daten beinhalten die Synthese und Charakterisierung neuartiger Actinid (Th, U, Np, Pu) Komplexe mit pyrrolbasierten Liganden, sowie ebenfalls die Ligandsynthese. Darunter fallen SC-XRD, NMR, IR, UV-VIS und EA Daten. Des weiteren quantenchemische Berechnungen zu den Systemen, sowie der Vergleich zum bereits bekannten Salen System.

Keywords: actinides; N donor ligands; bonding analysis; f electrons; pyrrole

Related publications

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Permalink: https://www.hzdr.de/publications/Publ-33353
Publ.-Id: 33353


Computational Science at HZDR: Tools, Services, and Consulting to Empower Your Research

Pape, D.; Lokamani, M.; Knodel, O.; Müller, S.; Huste, T.; Steinbach, P.; Juckeland, G.; Fiedler, M.

The Computational Science Department FWCC and its sister departments offer various tools and services to empower scientists at HZDR in their research. This presentation held at the 2021 PhD seminar aims at introducing the working groups DMS and MT-DMA as well as the Helmholtz Incubator Platforms HIFIS and Helmholtz AI, all hosted by FWCC, and the library FWCB. It presents a selection of said services and shows options of contact for receiving help in the topics presented.

Keywords: Computational Science; Research Software Engineering; High Performance Computing; Data Management; Machine Learning; Artificial Intelligence; Data Science

  • Lecture (others)
    PhD Seminar 2021, 18.10.2021, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-33351
Publ.-Id: 33351


Pages: [1.] [2.] [3.] [4.] [5.] [6.] [7.] [8.] [9.] [10.] [11.] [12.] [13.] [14.] [15.] [16.] [17.] [18.] [19.] [20.] [21.] [22.] [23.] [24.] [25.] [26.] [27.] [28.] [29.] [30.] [31.] [32.] [33.] [34.] [35.] [36.] [37.] [38.] [39.] [40.] [41.] [42.] [43.] [44.] [45.] [46.] [47.] [48.] [49.] [50.] [51.] [52.] [53.] [54.] [55.] [56.] [57.] [58.] [59.] [60.] [61.] [62.] [63.] [64.] [65.] [66.] [67.] [68.] [69.] [70.] [71.] [72.] [73.] [74.] [75.] [76.] [77.] [78.] [79.] [80.] [81.] [82.] [83.] [84.] [85.] [86.] [87.] [88.] [89.] [90.] [91.] [92.] [93.] [94.] [95.] [96.] [97.] [98.] [99.] [100.] [101.] [102.] [103.] [104.] [105.] [106.] [107.] [108.] [109.] [110.] [111.] [112.] [113.] [114.] [115.] [116.] [117.] [118.] [119.] [120.] [121.] [122.] [123.] [124.] [125.] [126.] [127.] [128.] [129.] [130.] [131.] [132.] [133.] [134.] [135.] [136.] [137.] [138.] [139.] [140.] [141.] [142.] [143.] [144.] [145.] [146.] [147.] [148.] [149.] [150.] [151.] [152.] [153.] [154.] [155.] [156.] [157.] [158.] [159.] [160.] [161.] [162.] [163.] [164.] [165.] [166.] [167.] [168.] [169.] [170.] [171.] [172.] [173.] [174.] [175.] [176.] [177.] [178.] [179.] [180.] [181.] [182.] [183.] [184.] [185.] [186.] [187.] [188.] [189.] [190.] [191.] [192.] [193.] [194.] [195.] [196.] [197.] [198.] [199.] [200.] [201.] [202.] [203.] [204.] [205.] [206.] [207.] [208.] [209.] [210.] [211.] [212.] [213.] [214.] [215.] [216.] [217.] [218.] [219.] [220.] [221.] [222.] [223.] [224.] [225.] [226.] [227.] [228.] [229.] [230.] [231.] [232.] [233.] [234.] [235.] [236.] [237.] [238.] [239.] [240.] [241.] [242.] [243.] [244.] [245.] [246.] [247.] [248.] [249.] [250.] [251.] [252.] [253.] [254.] [255.] [256.] [257.] [258.] [259.] [260.] [261.] [262.] [263.] [264.] [265.] [266.] [267.] [268.] [269.] [270.] [271.] [272.] [273.] [274.] [275.] [276.] [277.] [278.] [279.] [280.] [281.] [282.] [283.] [284.] [285.] [286.] [287.] [288.] [289.] [290.] [291.] [292.] [293.] [294.] [295.] [296.] [297.] [298.] [299.] [300.] [301.] [302.] [303.] [304.] [305.] [306.] [307.] [308.] [309.] [310.] [311.] [312.] [313.] [314.] [315.] [316.] [317.] [318.] [319.] [320.] [321.] [322.] [323.] [324.] [325.] [326.] [327.] [328.]